first

backend/internal/modules/auth/admin_handler.go

@@ -0,0 +1,130 @@
+package auth
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+
+	"backend/internal/modules/users"
+	"backend/internal/platform/middleware"
+	"backend/internal/platform/security"
+)
+
+const (
+	adminRefreshCookieName = "admin_refresh_token"
+	adminRefreshCookiePath = "/api/auth/admin"
+)
+
+// AdminHandler exposes the admin-space auth endpoints. It is kept entirely
+// separate from CustomerHandler: different cookie name, different cookie
+// path, different JWT audience, so an admin session can never be replayed
+// against a future customer-facing endpoint.
+type AdminHandler struct {
+	service      *Service
+	cookieSecure bool
+}
+
+func NewAdminHandler(service *Service, cookieSecure bool) *AdminHandler {
+	return &AdminHandler{service: service, cookieSecure: cookieSecure}
+}
+
+type loginRequest struct {
+	Email    string `json:"email" binding:"required,email"`
+	Password string `json:"password" binding:"required"`
+}
+
+type authUserResponse struct {
+	ID    uuid.UUID `json:"id"`
+	Email string    `json:"email"`
+	Role  string    `json:"role"`
+}
+
+type accessTokenResponse struct {
+	AccessToken string            `json:"access_token"`
+	User        *authUserResponse `json:"user,omitempty"`
+}
+
+func (h *AdminHandler) Login(c *gin.Context) {
+	var req loginRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+
+	pair, user, err := h.service.Login(c.Request.Context(), security.AudienceAdmin, users.RoleAdmin, req.Email, req.Password)
+	if err != nil {
+		h.respondLoginError(c, err)
+		return
+	}
+
+	h.setRefreshCookie(c, pair.RefreshToken)
+	c.JSON(http.StatusOK, accessTokenResponse{
+		AccessToken: pair.AccessToken,
+		User:        &authUserResponse{ID: user.ID, Email: user.Email, Role: user.Role},
+	})
+}
+
+func (h *AdminHandler) Refresh(c *gin.Context) {
+	token, err := c.Cookie(adminRefreshCookieName)
+	if err != nil || token == "" {
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "missing refresh token"})
+		return
+	}
+
+	pair, err := h.service.Refresh(c.Request.Context(), security.AudienceAdmin, token)
+	if err != nil {
+		h.clearRefreshCookie(c)
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid or expired refresh token"})
+		return
+	}
+
+	h.setRefreshCookie(c, pair.RefreshToken)
+	c.JSON(http.StatusOK, accessTokenResponse{AccessToken: pair.AccessToken})
+}
+
+func (h *AdminHandler) Logout(c *gin.Context) {
+	if token, err := c.Cookie(adminRefreshCookieName); err == nil && token != "" {
+		_ = h.service.Logout(c.Request.Context(), security.AudienceAdmin, token)
+	}
+	h.clearRefreshCookie(c)
+	c.JSON(http.StatusOK, gin.H{"message": "logged out"})
+}
+
+func (h *AdminHandler) Me(c *gin.Context) {
+	userID, ok := middleware.GetUserID(c)
+	if !ok {
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "unauthorized"})
+		return
+	}
+	user, err := h.service.Me(c.Request.Context(), userID)
+	if err != nil {
+		if errors.Is(err, users.ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "user not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to load user"})
+		return
+	}
+	c.JSON(http.StatusOK, authUserResponse{ID: user.ID, Email: user.Email, Role: user.Role})
+}
+
+func (h *AdminHandler) respondLoginError(c *gin.Context, err error) {
+	switch {
+	case errors.Is(err, ErrInvalidCredentials), errors.Is(err, ErrAccountDisabled):
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid credentials"})
+	default:
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "login failed"})
+	}
+}
+
+func (h *AdminHandler) setRefreshCookie(c *gin.Context, token string) {
+	c.SetSameSite(http.SameSiteStrictMode)
+	c.SetCookie(adminRefreshCookieName, token, int(h.service.RefreshTTL().Seconds()), adminRefreshCookiePath, "", h.cookieSecure, true)
+}
+
+func (h *AdminHandler) clearRefreshCookie(c *gin.Context) {
+	c.SetSameSite(http.SameSiteStrictMode)
+	c.SetCookie(adminRefreshCookieName, "", -1, adminRefreshCookiePath, "", h.cookieSecure, true)
+}

backend/internal/modules/auth/admin_routes.go

@@ -0,0 +1,14 @@
+package auth
+
+import "github.com/gin-gonic/gin"
+
+// RegisterAdminRoutes mounts the admin-space auth endpoints. loginRateLimit
+// is applied only to /login to blunt credential-stuffing/brute-force
+// attempts without throttling normal authenticated traffic.
+func RegisterAdminRoutes(rg *gin.RouterGroup, h *AdminHandler, requireAdmin gin.HandlerFunc, loginRateLimit gin.HandlerFunc) {
+	group := rg.Group("/auth/admin")
+	group.POST("/login", loginRateLimit, h.Login)
+	group.POST("/refresh", h.Refresh)
+	group.POST("/logout", h.Logout)
+	group.GET("/me", requireAdmin, h.Me)
+}

backend/internal/modules/auth/customer_handler.go

@@ -0,0 +1,112 @@
+package auth
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	"backend/internal/modules/users"
+	"backend/internal/platform/middleware"
+	"backend/internal/platform/security"
+)
+
+// customer cookie name/path are intentionally distinct from the admin ones
+// (see admin_handler.go) so the two spaces never share a session cookie.
+const (
+	customerRefreshCookieName = "customer_refresh_token"
+	customerRefreshCookiePath = "/api/auth/customer"
+)
+
+// CustomerHandler mirrors AdminHandler but issues/accepts only
+// customer-audience tokens. Not mounted by main.go in this phase (no
+// customer-facing module needs it yet) — it exists so the future
+// cart/orders module can activate customer auth without touching the admin
+// code path at all.
+type CustomerHandler struct {
+	service      *Service
+	cookieSecure bool
+}
+
+func NewCustomerHandler(service *Service, cookieSecure bool) *CustomerHandler {
+	return &CustomerHandler{service: service, cookieSecure: cookieSecure}
+}
+
+func (h *CustomerHandler) Login(c *gin.Context) {
+	var req loginRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+
+	pair, user, err := h.service.Login(c.Request.Context(), security.AudienceCustomer, users.RoleCustomer, req.Email, req.Password)
+	if err != nil {
+		switch {
+		case errors.Is(err, ErrInvalidCredentials), errors.Is(err, ErrAccountDisabled):
+			c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid credentials"})
+		default:
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "login failed"})
+		}
+		return
+	}
+
+	h.setRefreshCookie(c, pair.RefreshToken)
+	c.JSON(http.StatusOK, accessTokenResponse{
+		AccessToken: pair.AccessToken,
+		User:        &authUserResponse{ID: user.ID, Email: user.Email, Role: user.Role},
+	})
+}
+
+func (h *CustomerHandler) Refresh(c *gin.Context) {
+	token, err := c.Cookie(customerRefreshCookieName)
+	if err != nil || token == "" {
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "missing refresh token"})
+		return
+	}
+
+	pair, err := h.service.Refresh(c.Request.Context(), security.AudienceCustomer, token)
+	if err != nil {
+		h.clearRefreshCookie(c)
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid or expired refresh token"})
+		return
+	}
+
+	h.setRefreshCookie(c, pair.RefreshToken)
+	c.JSON(http.StatusOK, accessTokenResponse{AccessToken: pair.AccessToken})
+}
+
+func (h *CustomerHandler) Logout(c *gin.Context) {
+	if token, err := c.Cookie(customerRefreshCookieName); err == nil && token != "" {
+		_ = h.service.Logout(c.Request.Context(), security.AudienceCustomer, token)
+	}
+	h.clearRefreshCookie(c)
+	c.JSON(http.StatusOK, gin.H{"message": "logged out"})
+}
+
+func (h *CustomerHandler) Me(c *gin.Context) {
+	userID, ok := middleware.GetUserID(c)
+	if !ok {
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "unauthorized"})
+		return
+	}
+	user, err := h.service.Me(c.Request.Context(), userID)
+	if err != nil {
+		if errors.Is(err, users.ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "user not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to load user"})
+		return
+	}
+	c.JSON(http.StatusOK, authUserResponse{ID: user.ID, Email: user.Email, Role: user.Role})
+}
+
+func (h *CustomerHandler) setRefreshCookie(c *gin.Context, token string) {
+	c.SetSameSite(http.SameSiteStrictMode)
+	c.SetCookie(customerRefreshCookieName, token, int(h.service.RefreshTTL().Seconds()), customerRefreshCookiePath, "", h.cookieSecure, true)
+}
+
+func (h *CustomerHandler) clearRefreshCookie(c *gin.Context) {
+	c.SetSameSite(http.SameSiteStrictMode)
+	c.SetCookie(customerRefreshCookieName, "", -1, customerRefreshCookiePath, "", h.cookieSecure, true)
+}

backend/internal/modules/auth/customer_routes.go

@@ -0,0 +1,15 @@
+package auth
+
+import "github.com/gin-gonic/gin"
+
+// RegisterCustomerRoutes mounts the customer-space auth endpoints. Deliberately
+// NOT called from cmd/api/main.go in this phase: there is no customer-facing
+// module (cart/orders) yet, so exposing these routes today would just be a
+// dead surface. Wiring is ready for when that module is activated.
+func RegisterCustomerRoutes(rg *gin.RouterGroup, h *CustomerHandler, requireCustomer gin.HandlerFunc, loginRateLimit gin.HandlerFunc) {
+	group := rg.Group("/auth/customer")
+	group.POST("/login", loginRateLimit, h.Login)
+	group.POST("/refresh", h.Refresh)
+	group.POST("/logout", h.Logout)
+	group.GET("/me", requireCustomer, h.Me)
+}

backend/internal/modules/auth/model.go

@@ -0,0 +1,21 @@
+// Package auth issues and verifies sessions (access + refresh tokens) for
+// both the admin space and the (not-yet-mounted) customer space. It has no
+// database table of its own: user identity/credentials live in the users
+// module, and refresh-token/session state lives entirely in Redis.
+package auth
+
+import "errors"
+
+var (
+	ErrInvalidCredentials  = errors.New("invalid credentials")
+	ErrInvalidRefreshToken = errors.New("invalid refresh token")
+	ErrAccountDisabled     = errors.New("account disabled")
+)
+
+// TokenPair is returned to the client on login/refresh: the access token is
+// meant to be kept in memory by the frontend, the refresh token is meant to
+// be set as an httpOnly cookie by the handler (never returned to JS).
+type TokenPair struct {
+	AccessToken  string
+	RefreshToken string
+}

backend/internal/modules/auth/repository.go

@@ -0,0 +1,118 @@
+package auth
+
+import (
+	"context"
+	"crypto/rand"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/redis/go-redis/v9"
+
+	"backend/internal/platform/security"
+)
+
+// RefreshStore tracks live refresh tokens in Redis, scoped per audience
+// (admin/customer) so a session in one space is never visible to the other.
+type RefreshStore interface {
+	Issue(ctx context.Context, aud security.Audience, userID uuid.UUID, ttl time.Duration) (string, error)
+	Rotate(ctx context.Context, aud security.Audience, oldToken string, ttl time.Duration) (newToken string, userID uuid.UUID, err error)
+	Revoke(ctx context.Context, aud security.Audience, token string) error
+	RevokeAllForUser(ctx context.Context, aud security.Audience, userID uuid.UUID) error
+}
+
+type redisRefreshStore struct {
+	client *redis.Client
+}
+
+func NewRefreshStore(client *redis.Client) RefreshStore {
+	return &redisRefreshStore{client: client}
+}
+
+func sessionKey(aud security.Audience, token string) string {
+	return fmt.Sprintf("session:%s:%s", aud, token)
+}
+
+func userSetKey(aud security.Audience, userID uuid.UUID) string {
+	return fmt.Sprintf("session:%s:user:%s", aud, userID)
+}
+
+func randomToken() (string, error) {
+	buf := make([]byte, 32)
+	if _, err := rand.Read(buf); err != nil {
+		return "", err
+	}
+	return base64.RawURLEncoding.EncodeToString(buf), nil
+}
+
+func (s *redisRefreshStore) Issue(ctx context.Context, aud security.Audience, userID uuid.UUID, ttl time.Duration) (string, error) {
+	token, err := randomToken()
+	if err != nil {
+		return "", fmt.Errorf("generate refresh token: %w", err)
+	}
+	if err := s.client.Set(ctx, sessionKey(aud, token), userID.String(), ttl).Err(); err != nil {
+		return "", fmt.Errorf("store refresh token: %w", err)
+	}
+	// Best-effort secondary index for RevokeAllForUser; a token still present
+	// here after its primary key has naturally expired is harmless (RevokeAllForUser
+	// simply issues a DEL for an already-gone key).
+	s.client.SAdd(ctx, userSetKey(aud, userID), token)
+	return token, nil
+}
+
+func (s *redisRefreshStore) Rotate(ctx context.Context, aud security.Audience, oldToken string, ttl time.Duration) (string, uuid.UUID, error) {
+	val, err := s.client.GetDel(ctx, sessionKey(aud, oldToken)).Result()
+	if errors.Is(err, redis.Nil) {
+		return "", uuid.UUID{}, ErrInvalidRefreshToken
+	}
+	if err != nil {
+		return "", uuid.UUID{}, fmt.Errorf("lookup refresh token: %w", err)
+	}
+
+	userID, err := uuid.Parse(val)
+	if err != nil {
+		return "", uuid.UUID{}, fmt.Errorf("corrupt session value: %w", err)
+	}
+	s.client.SRem(ctx, userSetKey(aud, userID), oldToken)
+
+	newToken, err := s.Issue(ctx, aud, userID, ttl)
+	if err != nil {
+		return "", uuid.UUID{}, err
+	}
+	return newToken, userID, nil
+}
+
+func (s *redisRefreshStore) Revoke(ctx context.Context, aud security.Audience, token string) error {
+	val, err := s.client.GetDel(ctx, sessionKey(aud, token)).Result()
+	if errors.Is(err, redis.Nil) {
+		return nil // already revoked/expired: logout is idempotent
+	}
+	if err != nil {
+		return fmt.Errorf("revoke refresh token: %w", err)
+	}
+	if userID, parseErr := uuid.Parse(val); parseErr == nil {
+		s.client.SRem(ctx, userSetKey(aud, userID), token)
+	}
+	return nil
+}
+
+func (s *redisRefreshStore) RevokeAllForUser(ctx context.Context, aud security.Audience, userID uuid.UUID) error {
+	setKey := userSetKey(aud, userID)
+	tokens, err := s.client.SMembers(ctx, setKey).Result()
+	if err != nil {
+		return fmt.Errorf("list sessions: %w", err)
+	}
+	if len(tokens) > 0 {
+		keys := make([]string, len(tokens))
+		for i, t := range tokens {
+			keys[i] = sessionKey(aud, t)
+		}
+		if err := s.client.Del(ctx, keys...).Err(); err != nil {
+			return fmt.Errorf("revoke sessions: %w", err)
+		}
+	}
+	s.client.Del(ctx, setKey)
+	return nil
+}

backend/internal/modules/auth/service.go

@@ -0,0 +1,123 @@
+package auth
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/google/uuid"
+
+	"backend/internal/modules/users"
+	"backend/internal/platform/security"
+)
+
+// UserFinder is the minimal slice of the users module this service needs.
+// Defined here (consumer side) rather than depending on the full
+// users.Repository, so auth only ever reads user records, never writes them.
+type UserFinder interface {
+	FindByEmail(ctx context.Context, email string) (*users.User, error)
+	FindByID(ctx context.Context, id uuid.UUID) (*users.User, error)
+}
+
+type Service struct {
+	users      UserFinder
+	refresh    RefreshStore
+	jwtSecret  string
+	accessTTL  time.Duration
+	refreshTTL time.Duration
+}
+
+func NewService(userFinder UserFinder, refresh RefreshStore, jwtSecret string, accessTTL, refreshTTL time.Duration) *Service {
+	return &Service{
+		users:      userFinder,
+		refresh:    refresh,
+		jwtSecret:  jwtSecret,
+		accessTTL:  accessTTL,
+		refreshTTL: refreshTTL,
+	}
+}
+
+func (s *Service) RefreshTTL() time.Duration { return s.refreshTTL }
+
+// Login authenticates a user for a specific space (aud) and enforces that
+// the account's role matches that space (an admin account cannot log into
+// the customer space and vice versa, even before the customer module ships).
+func (s *Service) Login(ctx context.Context, aud security.Audience, expectedRole, email, password string) (*TokenPair, *users.User, error) {
+	user, err := s.users.FindByEmail(ctx, email)
+	if err != nil {
+		if errors.Is(err, users.ErrNotFound) {
+			return nil, nil, ErrInvalidCredentials
+		}
+		return nil, nil, err
+	}
+
+	if !user.IsActive {
+		return nil, nil, ErrAccountDisabled
+	}
+	if user.Role != expectedRole {
+		return nil, nil, ErrInvalidCredentials
+	}
+
+	ok, err := security.VerifyPassword(user.PasswordHash, password)
+	if err != nil || !ok {
+		return nil, nil, ErrInvalidCredentials
+	}
+
+	pair, err := s.issuePair(ctx, aud, user)
+	if err != nil {
+		return nil, nil, err
+	}
+	return pair, user, nil
+}
+
+// Refresh rotates a refresh token (single use) and issues a fresh pair. If
+// the presented token is unknown to the store (already used, revoked, or
+// expired) it is treated as invalid; genuine reuse of a stolen token simply
+// fails from that point on since the old token was deleted at issuance time.
+func (s *Service) Refresh(ctx context.Context, aud security.Audience, refreshToken string) (*TokenPair, error) {
+	newRefreshToken, userID, err := s.refresh.Rotate(ctx, aud, refreshToken, s.refreshTTL)
+	if err != nil {
+		return nil, err
+	}
+
+	user, err := s.users.FindByID(ctx, userID)
+	if err != nil {
+		return nil, fmt.Errorf("lookup user for refresh: %w", err)
+	}
+	if !user.IsActive {
+		_ = s.refresh.RevokeAllForUser(ctx, aud, userID)
+		return nil, ErrAccountDisabled
+	}
+
+	access, err := security.IssueAccessToken(s.jwtSecret, s.accessTTL, user.ID, user.Role, aud)
+	if err != nil {
+		return nil, fmt.Errorf("issue access token: %w", err)
+	}
+
+	return &TokenPair{AccessToken: access, RefreshToken: newRefreshToken}, nil
+}
+
+func (s *Service) Logout(ctx context.Context, aud security.Audience, refreshToken string) error {
+	return s.refresh.Revoke(ctx, aud, refreshToken)
+}
+
+func (s *Service) LogoutAll(ctx context.Context, aud security.Audience, userID uuid.UUID) error {
+	return s.refresh.RevokeAllForUser(ctx, aud, userID)
+}
+
+func (s *Service) Me(ctx context.Context, userID uuid.UUID) (*users.User, error) {
+	return s.users.FindByID(ctx, userID)
+}
+
+func (s *Service) issuePair(ctx context.Context, aud security.Audience, user *users.User) (*TokenPair, error) {
+	access, err := security.IssueAccessToken(s.jwtSecret, s.accessTTL, user.ID, user.Role, aud)
+	if err != nil {
+		return nil, fmt.Errorf("issue access token: %w", err)
+	}
+	refreshToken, err := s.refresh.Issue(ctx, aud, user.ID, s.refreshTTL)
+	if err != nil {
+		return nil, fmt.Errorf("issue refresh token: %w", err)
+	}
+	return &TokenPair{AccessToken: access, RefreshToken: refreshToken}, nil
+}

backend/internal/modules/categories/handler.go

@@ -0,0 +1,167 @@
+package categories
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+)
+
+type Handler struct {
+	service *Service
+}
+
+func NewHandler(service *Service) *Handler {
+	return &Handler{service: service}
+}
+
+type categoryResponse struct {
+	ID          uuid.UUID `json:"id"`
+	Name        string    `json:"name"`
+	Slug        string    `json:"slug"`
+	Description string    `json:"description"`
+	Position    int       `json:"position"`
+	IsActive    bool      `json:"is_active"`
+}
+
+func toResponse(cat *Category) categoryResponse {
+	return categoryResponse{
+		ID:          cat.ID,
+		Name:        cat.Name,
+		Slug:        cat.Slug,
+		Description: cat.Description,
+		Position:    cat.Position,
+		IsActive:    cat.IsActive,
+	}
+}
+
+// ListAdmin returns every category (active or not).
+func (h *Handler) ListAdmin(c *gin.Context) {
+	list, err := h.service.List(c.Request.Context(), false)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to list categories"})
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"categories": toResponseList(list)})
+}
+
+// ListPublic returns only active categories, for storefront navigation.
+func (h *Handler) ListPublic(c *gin.Context) {
+	list, err := h.service.List(c.Request.Context(), true)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to list categories"})
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"categories": toResponseList(list)})
+}
+
+func toResponseList(list []*Category) []categoryResponse {
+	resp := make([]categoryResponse, 0, len(list))
+	for _, cat := range list {
+		resp = append(resp, toResponse(cat))
+	}
+	return resp
+}
+
+type upsertRequest struct {
+	Name        string `json:"name" binding:"required"`
+	Slug        string `json:"slug" binding:"required"`
+	Description string `json:"description"`
+	Position    int    `json:"position"`
+	IsActive    bool   `json:"is_active"`
+}
+
+func (h *Handler) Create(c *gin.Context) {
+	var req upsertRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	cat, err := h.service.Create(c.Request.Context(), req.Name, req.Slug, req.Description, req.Position, req.IsActive)
+	if err != nil {
+		if errors.Is(err, ErrSlugTaken) {
+			c.JSON(http.StatusConflict, gin.H{"error": "slug already in use"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to create category"})
+		return
+	}
+	c.JSON(http.StatusCreated, toResponse(cat))
+}
+
+func (h *Handler) Update(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	var req upsertRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	cat, err := h.service.Update(c.Request.Context(), id, req.Name, req.Slug, req.Description, req.Position, req.IsActive)
+	if err != nil {
+		switch {
+		case errors.Is(err, ErrNotFound):
+			c.JSON(http.StatusNotFound, gin.H{"error": "category not found"})
+		case errors.Is(err, ErrSlugTaken):
+			c.JSON(http.StatusConflict, gin.H{"error": "slug already in use"})
+		default:
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to update category"})
+		}
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(cat))
+}
+
+type updatePositionRequest struct {
+	Position int `json:"position"`
+}
+
+// UpdatePosition lets the admin reorder the category display order (e.g.
+// move up/move down in the admin list) without resending the whole
+// category payload.
+func (h *Handler) UpdatePosition(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	var req updatePositionRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	cat, err := h.service.UpdatePosition(c.Request.Context(), id, req.Position)
+	if err != nil {
+		if errors.Is(err, ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "category not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to update position"})
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(cat))
+}
+
+func (h *Handler) Delete(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	if err := h.service.Delete(c.Request.Context(), id); err != nil {
+		switch {
+		case errors.Is(err, ErrNotFound):
+			c.JSON(http.StatusNotFound, gin.H{"error": "category not found"})
+		case errors.Is(err, ErrInUse):
+			c.JSON(http.StatusConflict, gin.H{"error": "category is used by existing products"})
+		default:
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to delete category"})
+		}
+		return
+	}
+	c.Status(http.StatusNoContent)
+}

backend/internal/modules/categories/model.go

@@ -0,0 +1,22 @@
+// Package categories lets the admin organize products into their own
+// categories (name, slug, description, ordering) without touching code.
+package categories
+
+import (
+	"time"
+
+	"github.com/google/uuid"
+)
+
+type Category struct {
+	ID          uuid.UUID `gorm:"type:uuid;primaryKey"`
+	Name        string    `gorm:"not null"`
+	Slug        string    `gorm:"uniqueIndex;not null"`
+	Description string    `gorm:"not null;default:''"`
+	Position    int       `gorm:"not null;default:0"`
+	IsActive    bool      `gorm:"not null;default:true"`
+	CreatedAt   time.Time
+	UpdatedAt   time.Time
+}
+
+func (Category) TableName() string { return "categories" }

backend/internal/modules/categories/repository.go

@@ -0,0 +1,98 @@
+package categories
+
+import (
+	"context"
+	"errors"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgconn"
+	"gorm.io/gorm"
+)
+
+var (
+	ErrNotFound  = errors.New("category not found")
+	ErrSlugTaken = errors.New("slug already in use")
+	ErrInUse     = errors.New("category is referenced by existing products")
+)
+
+type Repository interface {
+	Create(ctx context.Context, cat *Category) error
+	FindByID(ctx context.Context, id uuid.UUID) (*Category, error)
+	List(ctx context.Context, activeOnly bool) ([]*Category, error)
+	Update(ctx context.Context, cat *Category) error
+	Delete(ctx context.Context, id uuid.UUID) error
+}
+
+type gormRepository struct {
+	db *gorm.DB
+}
+
+func NewRepository(db *gorm.DB) Repository {
+	return &gormRepository{db: db}
+}
+
+func (r *gormRepository) Create(ctx context.Context, cat *Category) error {
+	if err := r.db.WithContext(ctx).Create(cat).Error; err != nil {
+		if isUniqueViolation(err) {
+			return ErrSlugTaken
+		}
+		return err
+	}
+	return nil
+}
+
+func (r *gormRepository) FindByID(ctx context.Context, id uuid.UUID) (*Category, error) {
+	var cat Category
+	err := r.db.WithContext(ctx).Where("id = ?", id).First(&cat).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &cat, nil
+}
+
+func (r *gormRepository) List(ctx context.Context, activeOnly bool) ([]*Category, error) {
+	q := r.db.WithContext(ctx).Order("position asc, name asc")
+	if activeOnly {
+		q = q.Where("is_active = ?", true)
+	}
+	var list []*Category
+	if err := q.Find(&list).Error; err != nil {
+		return nil, err
+	}
+	return list, nil
+}
+
+func (r *gormRepository) Update(ctx context.Context, cat *Category) error {
+	err := r.db.WithContext(ctx).Save(cat).Error
+	if isUniqueViolation(err) {
+		return ErrSlugTaken
+	}
+	return err
+}
+
+func (r *gormRepository) Delete(ctx context.Context, id uuid.UUID) error {
+	res := r.db.WithContext(ctx).Delete(&Category{}, "id = ?", id)
+	if res.Error != nil {
+		if isForeignKeyViolation(res.Error) {
+			return ErrInUse
+		}
+		return res.Error
+	}
+	if res.RowsAffected == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
+func isUniqueViolation(err error) bool {
+	var pgErr *pgconn.PgError
+	return errors.As(err, &pgErr) && pgErr.Code == "23505"
+}
+
+func isForeignKeyViolation(err error) bool {
+	var pgErr *pgconn.PgError
+	return errors.As(err, &pgErr) && pgErr.Code == "23503"
+}

backend/internal/modules/categories/routes.go

@@ -0,0 +1,18 @@
+package categories
+
+import "github.com/gin-gonic/gin"
+
+func RegisterAdminRoutes(rg *gin.RouterGroup, h *Handler, requireAdmin gin.HandlerFunc) {
+	group := rg.Group("/admin/categories", requireAdmin)
+	group.GET("", h.ListAdmin)
+	group.POST("", h.Create)
+	group.PUT("/:id", h.Update)
+	group.PATCH("/:id/position", h.UpdatePosition)
+	group.DELETE("/:id", h.Delete)
+}
+
+// RegisterPublicRoutes exposes the read-only, active-only category list
+// used by the storefront navigation/filtering.
+func RegisterPublicRoutes(rg *gin.RouterGroup, h *Handler) {
+	rg.GET("/categories", h.ListPublic)
+}

backend/internal/modules/categories/service.go

@@ -0,0 +1,72 @@
+package categories
+
+import (
+	"context"
+
+	"github.com/google/uuid"
+)
+
+type Service struct {
+	repo Repository
+}
+
+func NewService(repo Repository) *Service {
+	return &Service{repo: repo}
+}
+
+func (s *Service) List(ctx context.Context, activeOnly bool) ([]*Category, error) {
+	return s.repo.List(ctx, activeOnly)
+}
+
+func (s *Service) Get(ctx context.Context, id uuid.UUID) (*Category, error) {
+	return s.repo.FindByID(ctx, id)
+}
+
+func (s *Service) Create(ctx context.Context, name, slug, description string, position int, isActive bool) (*Category, error) {
+	cat := &Category{
+		ID:          uuid.New(),
+		Name:        name,
+		Slug:        slug,
+		Description: description,
+		Position:    position,
+		IsActive:    isActive,
+	}
+	if err := s.repo.Create(ctx, cat); err != nil {
+		return nil, err
+	}
+	return cat, nil
+}
+
+func (s *Service) Update(ctx context.Context, id uuid.UUID, name, slug, description string, position int, isActive bool) (*Category, error) {
+	cat, err := s.repo.FindByID(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	cat.Name = name
+	cat.Slug = slug
+	cat.Description = description
+	cat.Position = position
+	cat.IsActive = isActive
+	if err := s.repo.Update(ctx, cat); err != nil {
+		return nil, err
+	}
+	return cat, nil
+}
+
+func (s *Service) Delete(ctx context.Context, id uuid.UUID) error {
+	return s.repo.Delete(ctx, id)
+}
+
+// UpdatePosition lets the admin reorder the catalog display order without
+// resending the full category payload.
+func (s *Service) UpdatePosition(ctx context.Context, id uuid.UUID, position int) (*Category, error) {
+	cat, err := s.repo.FindByID(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	cat.Position = position
+	if err := s.repo.Update(ctx, cat); err != nil {
+		return nil, err
+	}
+	return cat, nil
+}

backend/internal/modules/media/handler.go

@@ -0,0 +1,126 @@
+package media
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+)
+
+type Handler struct {
+	service *Service
+}
+
+func NewHandler(service *Service) *Handler {
+	return &Handler{service: service}
+}
+
+type mediaResponse struct {
+	ID        uuid.UUID `json:"id"`
+	Filename  string    `json:"filename"`
+	URL       string    `json:"url"`
+	MimeType  string    `json:"mime_type"`
+	SizeBytes int64     `json:"size_bytes"`
+	AltText   string    `json:"alt_text"`
+}
+
+func toResponse(m *Media) mediaResponse {
+	return mediaResponse{
+		ID:        m.ID,
+		Filename:  m.Filename,
+		URL:       m.URL,
+		MimeType:  m.MimeType,
+		SizeBytes: m.SizeBytes,
+		AltText:   m.AltText,
+	}
+}
+
+func (h *Handler) List(c *gin.Context) {
+	list, err := h.service.List(c.Request.Context())
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to list media"})
+		return
+	}
+	resp := make([]mediaResponse, 0, len(list))
+	for _, m := range list {
+		resp = append(resp, toResponse(m))
+	}
+	c.JSON(http.StatusOK, gin.H{"media": resp})
+}
+
+func (h *Handler) Upload(c *gin.Context) {
+	fileHeader, err := c.FormFile("file")
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "missing file field"})
+		return
+	}
+
+	file, err := fileHeader.Open()
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "failed to open uploaded file"})
+		return
+	}
+	defer file.Close()
+
+	contentType := fileHeader.Header.Get("Content-Type")
+	altText := c.PostForm("alt_text")
+
+	m, err := h.service.Upload(c.Request.Context(), fileHeader.Filename, file, fileHeader.Size, contentType, altText)
+	if err != nil {
+		switch {
+		case errors.Is(err, ErrFileTooLarge):
+			c.JSON(http.StatusRequestEntityTooLarge, gin.H{"error": "file exceeds the maximum allowed size"})
+		case errors.Is(err, ErrUnsupportedType):
+			c.JSON(http.StatusUnsupportedMediaType, gin.H{"error": "unsupported file type"})
+		default:
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to upload file"})
+		}
+		return
+	}
+	c.JSON(http.StatusCreated, toResponse(m))
+}
+
+type updateRequest struct {
+	AltText string `json:"alt_text"`
+}
+
+func (h *Handler) Update(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	var req updateRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	m, err := h.service.UpdateAltText(c.Request.Context(), id, req.AltText)
+	if err != nil {
+		if errors.Is(err, ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "media not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to update media"})
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(m))
+}
+
+func (h *Handler) Delete(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	if err := h.service.Delete(c.Request.Context(), id); err != nil {
+		if errors.Is(err, ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "media not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to delete media"})
+		return
+	}
+	c.Status(http.StatusNoContent)
+}

backend/internal/modules/media/model.go

@@ -0,0 +1,24 @@
+// Package media manages uploaded files (images/videos) and abstracts the
+// storage backend behind a Storage interface so the admin can switch
+// between local disk and any S3-compatible bucket via configuration only.
+package media
+
+import (
+	"time"
+
+	"github.com/google/uuid"
+)
+
+type Media struct {
+	ID         uuid.UUID `gorm:"type:uuid;primaryKey"`
+	Filename   string    `gorm:"not null"`
+	StorageKey string    `gorm:"not null"`
+	URL        string    `gorm:"not null"`
+	MimeType   string    `gorm:"not null"`
+	SizeBytes  int64     `gorm:"not null"`
+	AltText    string    `gorm:"not null;default:''"`
+	CreatedAt  time.Time
+	UpdatedAt  time.Time
+}
+
+func (Media) TableName() string { return "media" }

backend/internal/modules/media/repository.go

@@ -0,0 +1,66 @@
+package media
+
+import (
+	"context"
+	"errors"
+
+	"github.com/google/uuid"
+	"gorm.io/gorm"
+)
+
+var ErrNotFound = errors.New("media not found")
+
+type Repository interface {
+	Create(ctx context.Context, m *Media) error
+	FindByID(ctx context.Context, id uuid.UUID) (*Media, error)
+	List(ctx context.Context) ([]*Media, error)
+	Update(ctx context.Context, m *Media) error
+	Delete(ctx context.Context, id uuid.UUID) error
+}
+
+type gormRepository struct {
+	db *gorm.DB
+}
+
+func NewRepository(db *gorm.DB) Repository {
+	return &gormRepository{db: db}
+}
+
+func (r *gormRepository) Create(ctx context.Context, m *Media) error {
+	return r.db.WithContext(ctx).Create(m).Error
+}
+
+func (r *gormRepository) FindByID(ctx context.Context, id uuid.UUID) (*Media, error) {
+	var m Media
+	err := r.db.WithContext(ctx).Where("id = ?", id).First(&m).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &m, nil
+}
+
+func (r *gormRepository) List(ctx context.Context) ([]*Media, error) {
+	var list []*Media
+	if err := r.db.WithContext(ctx).Order("created_at desc").Find(&list).Error; err != nil {
+		return nil, err
+	}
+	return list, nil
+}
+
+func (r *gormRepository) Update(ctx context.Context, m *Media) error {
+	return r.db.WithContext(ctx).Save(m).Error
+}
+
+func (r *gormRepository) Delete(ctx context.Context, id uuid.UUID) error {
+	res := r.db.WithContext(ctx).Delete(&Media{}, "id = ?", id)
+	if res.Error != nil {
+		return res.Error
+	}
+	if res.RowsAffected == 0 {
+		return ErrNotFound
+	}
+	return nil
+}

backend/internal/modules/media/routes.go

@@ -0,0 +1,11 @@
+package media
+
+import "github.com/gin-gonic/gin"
+
+func RegisterAdminRoutes(rg *gin.RouterGroup, h *Handler, requireAdmin gin.HandlerFunc) {
+	group := rg.Group("/admin/media", requireAdmin)
+	group.GET("", h.List)
+	group.POST("", h.Upload)
+	group.PUT("/:id", h.Update)
+	group.DELETE("/:id", h.Delete)
+}

backend/internal/modules/media/service.go

@@ -0,0 +1,99 @@
+package media
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+
+	"github.com/google/uuid"
+)
+
+var (
+	ErrFileTooLarge    = errors.New("file exceeds the maximum allowed size")
+	ErrUnsupportedType = errors.New("unsupported file type")
+)
+
+// allowedTypes maps accepted MIME types to a safe file extension. Anything
+// not in this list is rejected -- uploads are never trusted to declare
+// their own extension.
+var allowedTypes = map[string]string{
+	"image/jpeg": ".jpg",
+	"image/png":  ".png",
+	"image/webp": ".webp",
+	"image/gif":  ".gif",
+	"video/mp4":  ".mp4",
+	"video/webm": ".webm",
+}
+
+type Service struct {
+	repo        Repository
+	storage     Storage
+	maxSizeByte int64
+}
+
+func NewService(repo Repository, storage Storage, maxSizeBytes int64) *Service {
+	return &Service{repo: repo, storage: storage, maxSizeByte: maxSizeBytes}
+}
+
+func (s *Service) List(ctx context.Context) ([]*Media, error) {
+	return s.repo.List(ctx)
+}
+
+func (s *Service) Get(ctx context.Context, id uuid.UUID) (*Media, error) {
+	return s.repo.FindByID(ctx, id)
+}
+
+func (s *Service) Upload(ctx context.Context, filename string, reader io.Reader, size int64, contentType, altText string) (*Media, error) {
+	if size > s.maxSizeByte {
+		return nil, ErrFileTooLarge
+	}
+	ext, ok := allowedTypes[contentType]
+	if !ok {
+		return nil, ErrUnsupportedType
+	}
+
+	key := uuid.NewString() + ext
+	url, err := s.storage.Save(ctx, key, reader, size, contentType)
+	if err != nil {
+		return nil, fmt.Errorf("save file: %w", err)
+	}
+
+	m := &Media{
+		ID:         uuid.New(),
+		Filename:   filename,
+		StorageKey: key,
+		URL:        url,
+		MimeType:   contentType,
+		SizeBytes:  size,
+		AltText:    altText,
+	}
+	if err := s.repo.Create(ctx, m); err != nil {
+		_ = s.storage.Delete(ctx, key)
+		return nil, fmt.Errorf("save metadata: %w", err)
+	}
+	return m, nil
+}
+
+func (s *Service) UpdateAltText(ctx context.Context, id uuid.UUID, altText string) (*Media, error) {
+	m, err := s.repo.FindByID(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	m.AltText = altText
+	if err := s.repo.Update(ctx, m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
+func (s *Service) Delete(ctx context.Context, id uuid.UUID) error {
+	m, err := s.repo.FindByID(ctx, id)
+	if err != nil {
+		return err
+	}
+	if err := s.storage.Delete(ctx, m.StorageKey); err != nil {
+		return fmt.Errorf("delete stored file: %w", err)
+	}
+	return s.repo.Delete(ctx, id)
+}

backend/internal/modules/media/storage.go

@@ -0,0 +1,19 @@
+package media
+
+import (
+	"context"
+	"io"
+)
+
+// Storage is the pluggable backend that actually persists uploaded bytes.
+// The service/handler layers never know whether files end up on local disk
+// or in an S3 bucket -- only main.go decides which implementation to wire
+// in, based on MEDIA_STORAGE_DRIVER.
+type Storage interface {
+	// Save persists the content under the given key and returns the
+	// publicly reachable URL for it.
+	Save(ctx context.Context, key string, reader io.Reader, size int64, contentType string) (url string, err error)
+	// Delete removes the object identified by key. Deleting a
+	// already-removed key must not be treated as an error.
+	Delete(ctx context.Context, key string) error
+}

backend/internal/modules/media/storage_local.go

@@ -0,0 +1,51 @@
+package media
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// LocalStorage saves uploads under a directory on disk and serves them via
+// a static file route (mounted by main.go at /uploads when this driver is
+// active).
+type LocalStorage struct {
+	dir     string
+	baseURL string
+}
+
+func NewLocalStorage(dir, baseURL string) (*LocalStorage, error) {
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return nil, fmt.Errorf("create upload dir: %w", err)
+	}
+	return &LocalStorage{dir: dir, baseURL: strings.TrimRight(baseURL, "/")}, nil
+}
+
+func (s *LocalStorage) Save(_ context.Context, key string, reader io.Reader, _ int64, _ string) (string, error) {
+	// key is always a freshly generated UUID-based name (see service.go),
+	// never derived from user input, so path traversal is not reachable here.
+	dest := filepath.Join(s.dir, filepath.Base(key))
+
+	f, err := os.OpenFile(dest, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o644)
+	if err != nil {
+		return "", fmt.Errorf("create file: %w", err)
+	}
+	defer f.Close()
+
+	if _, err := io.Copy(f, reader); err != nil {
+		return "", fmt.Errorf("write file: %w", err)
+	}
+
+	return s.baseURL + "/" + filepath.Base(key), nil
+}
+
+func (s *LocalStorage) Delete(_ context.Context, key string) error {
+	err := os.Remove(filepath.Join(s.dir, filepath.Base(key)))
+	if err != nil && !os.IsNotExist(err) {
+		return fmt.Errorf("delete file: %w", err)
+	}
+	return nil
+}

backend/internal/modules/media/storage_s3.go

@@ -0,0 +1,89 @@
+package media
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+
+	awsconfig "github.com/aws/aws-sdk-go-v2/config"
+	"github.com/aws/aws-sdk-go-v2/credentials"
+	"github.com/aws/aws-sdk-go-v2/service/s3"
+	"github.com/aws/smithy-go"
+)
+
+// S3Config holds the settings needed to talk to any S3-compatible bucket
+// (AWS S3 itself, MinIO, Cloudflare R2, ...).
+type S3Config struct {
+	Bucket        string
+	Region        string
+	Endpoint      string // leave empty for real AWS S3
+	AccessKeyID   string
+	SecretKey     string
+	UsePathStyle  bool
+	PublicBaseURL string // e.g. https://cdn.example.com or https://bucket.s3.region.amazonaws.com
+}
+
+type S3Storage struct {
+	client  *s3.Client
+	bucket  string
+	baseURL string
+}
+
+func NewS3Storage(ctx context.Context, cfg S3Config) (*S3Storage, error) {
+	awsCfg, err := awsconfig.LoadDefaultConfig(ctx,
+		awsconfig.WithRegion(cfg.Region),
+		awsconfig.WithCredentialsProvider(credentials.NewStaticCredentialsProvider(cfg.AccessKeyID, cfg.SecretKey, "")),
+	)
+	if err != nil {
+		return nil, fmt.Errorf("load aws config: %w", err)
+	}
+
+	client := s3.NewFromConfig(awsCfg, func(o *s3.Options) {
+		if cfg.Endpoint != "" {
+			o.BaseEndpoint = &cfg.Endpoint
+		}
+		o.UsePathStyle = cfg.UsePathStyle
+	})
+
+	baseURL := cfg.PublicBaseURL
+	if baseURL == "" {
+		if cfg.Endpoint != "" {
+			baseURL = strings.TrimRight(cfg.Endpoint, "/") + "/" + cfg.Bucket
+		} else {
+			baseURL = fmt.Sprintf("https://%s.s3.%s.amazonaws.com", cfg.Bucket, cfg.Region)
+		}
+	}
+
+	return &S3Storage{client: client, bucket: cfg.Bucket, baseURL: strings.TrimRight(baseURL, "/")}, nil
+}
+
+func (s *S3Storage) Save(ctx context.Context, key string, reader io.Reader, size int64, contentType string) (string, error) {
+	_, err := s.client.PutObject(ctx, &s3.PutObjectInput{
+		Bucket:        &s.bucket,
+		Key:           &key,
+		Body:          reader,
+		ContentType:   &contentType,
+		ContentLength: &size,
+	})
+	if err != nil {
+		return "", fmt.Errorf("s3 put object: %w", err)
+	}
+	return s.baseURL + "/" + key, nil
+}
+
+func (s *S3Storage) Delete(ctx context.Context, key string) error {
+	_, err := s.client.DeleteObject(ctx, &s3.DeleteObjectInput{
+		Bucket: &s.bucket,
+		Key:    &key,
+	})
+	if err != nil {
+		var apiErr smithy.APIError
+		if errors.As(err, &apiErr) && apiErr.ErrorCode() == "NoSuchKey" {
+			return nil
+		}
+		return fmt.Errorf("s3 delete object: %w", err)
+	}
+	return nil
+}

backend/internal/modules/orders/handler.go

@@ -0,0 +1,185 @@
+package orders
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+
+	"backend/internal/modules/pricing"
+	"backend/internal/modules/products"
+)
+
+type Handler struct {
+	service *Service
+}
+
+func NewHandler(service *Service) *Handler {
+	return &Handler{service: service}
+}
+
+type itemRequest struct {
+	ProductID   uuid.UUID `json:"product_id" binding:"required"`
+	PriceTierID uuid.UUID `json:"price_tier_id" binding:"required"`
+	Multiplier  int64     `json:"multiplier" binding:"required,gte=1"`
+}
+
+type createRequest struct {
+	CustomerName  string        `json:"customer_name" binding:"required"`
+	CustomerEmail string        `json:"customer_email" binding:"required,email"`
+	CustomerPhone string        `json:"customer_phone"`
+	Notes         string        `json:"notes"`
+	Items         []itemRequest `json:"items" binding:"required,min=1,dive"`
+}
+
+type orderItemResponse struct {
+	ProductID      *uuid.UUID `json:"product_id,omitempty"`
+	ProductName    string     `json:"product_name"`
+	UnitSymbol     string     `json:"unit_symbol"`
+	TierQuantity   float64    `json:"tier_quantity"`
+	Multiplier     int64      `json:"multiplier"`
+	UnitPriceCents int64      `json:"unit_price_cents"`
+	TotalCents     int64      `json:"total_cents"`
+}
+
+type orderResponse struct {
+	ID            uuid.UUID           `json:"id"`
+	CustomerName  string              `json:"customer_name"`
+	CustomerEmail string              `json:"customer_email"`
+	CustomerPhone string              `json:"customer_phone"`
+	Status        string              `json:"status"`
+	TotalCents    int64               `json:"total_cents"`
+	Notes         string              `json:"notes"`
+	Items         []orderItemResponse `json:"items,omitempty"`
+}
+
+func toResponse(order *Order, items []*OrderItem) orderResponse {
+	resp := orderResponse{
+		ID:            order.ID,
+		CustomerName:  order.CustomerName,
+		CustomerEmail: order.CustomerEmail,
+		CustomerPhone: order.CustomerPhone,
+		Status:        order.Status,
+		TotalCents:    order.TotalCents,
+		Notes:         order.Notes,
+	}
+	for _, item := range items {
+		resp.Items = append(resp.Items, orderItemResponse{
+			ProductID:      item.ProductID,
+			ProductName:    item.ProductName,
+			UnitSymbol:     item.UnitSymbol,
+			TierQuantity:   item.TierQuantity,
+			Multiplier:     item.Multiplier,
+			UnitPriceCents: item.UnitPriceCents,
+			TotalCents:     item.TotalCents,
+		})
+	}
+	return resp
+}
+
+// Create is public: a visitor (connected or not, per spec section 17) can
+// place an order without an account.
+func (h *Handler) Create(c *gin.Context) {
+	var req createRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+
+	items := make([]ItemInput, 0, len(req.Items))
+	for _, item := range req.Items {
+		items = append(items, ItemInput{
+			ProductID:   item.ProductID,
+			PriceTierID: item.PriceTierID,
+			Multiplier:  item.Multiplier,
+		})
+	}
+
+	order, orderItems, err := h.service.Create(c.Request.Context(), CreateInput{
+		CustomerName:  req.CustomerName,
+		CustomerEmail: req.CustomerEmail,
+		CustomerPhone: req.CustomerPhone,
+		Notes:         req.Notes,
+		Items:         items,
+	})
+	if err != nil {
+		h.respondCreateError(c, err)
+		return
+	}
+	c.JSON(http.StatusCreated, toResponse(order, orderItems))
+}
+
+func (h *Handler) respondCreateError(c *gin.Context, err error) {
+	switch {
+	case errors.Is(err, ErrEmptyOrder), errors.Is(err, ErrProductMismatch):
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+	case errors.Is(err, pricing.ErrNotFound):
+		c.JSON(http.StatusBadRequest, gin.H{"error": "unknown price tier"})
+	case errors.Is(err, products.ErrNotFound):
+		c.JSON(http.StatusBadRequest, gin.H{"error": "unknown product"})
+	default:
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to create order"})
+	}
+}
+
+func (h *Handler) ListAdmin(c *gin.Context) {
+	list, err := h.service.List(c.Request.Context(), c.Query("status"))
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to list orders"})
+		return
+	}
+	resp := make([]orderResponse, 0, len(list))
+	for _, order := range list {
+		resp = append(resp, toResponse(order, nil))
+	}
+	c.JSON(http.StatusOK, gin.H{"orders": resp})
+}
+
+func (h *Handler) GetAdmin(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	order, items, err := h.service.Get(c.Request.Context(), id)
+	if err != nil {
+		if errors.Is(err, ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "order not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to load order"})
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(order, items))
+}
+
+type updateStatusRequest struct {
+	Status string `json:"status" binding:"required"`
+}
+
+func (h *Handler) UpdateStatus(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	var req updateStatusRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	order, err := h.service.UpdateStatus(c.Request.Context(), id, req.Status)
+	if err != nil {
+		switch {
+		case errors.Is(err, ErrNotFound):
+			c.JSON(http.StatusNotFound, gin.H{"error": "order not found"})
+		case errors.Is(err, ErrInvalidStatus):
+			c.JSON(http.StatusBadRequest, gin.H{"error": "invalid status"})
+		default:
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to update order status"})
+		}
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(order, nil))
+}

backend/internal/modules/orders/model.go

@@ -0,0 +1,63 @@
+// Package orders lets a customer (connected or not, per spec section 17-19)
+// place an order directly from the storefront, and lets the admin track
+// and update it. Pricing is never trusted from the client: each line is
+// resolved against the pricing module's authoritative price tier at
+// creation time.
+package orders
+
+import (
+	"time"
+
+	"github.com/google/uuid"
+)
+
+const (
+	StatusPending   = "pending"
+	StatusConfirmed = "confirmed"
+	StatusPreparing = "preparing"
+	StatusShipped   = "shipped"
+	StatusCompleted = "completed"
+	StatusCancelled = "cancelled"
+)
+
+var ValidStatuses = map[string]bool{
+	StatusPending:   true,
+	StatusConfirmed: true,
+	StatusPreparing: true,
+	StatusShipped:   true,
+	StatusCompleted: true,
+	StatusCancelled: true,
+}
+
+type Order struct {
+	ID            uuid.UUID `gorm:"type:uuid;primaryKey"`
+	CustomerName  string    `gorm:"not null"`
+	CustomerEmail string    `gorm:"not null"`
+	CustomerPhone string    `gorm:"not null;default:''"`
+	Status        string    `gorm:"not null;default:pending"`
+	TotalCents    int64     `gorm:"not null;default:0"`
+	Notes         string    `gorm:"not null;default:''"`
+	CreatedAt     time.Time
+	UpdatedAt     time.Time
+}
+
+func (Order) TableName() string { return "orders" }
+
+// OrderItem snapshots the product name, unit symbol and unit price at order
+// time, so the order stays accurate even if the product/unit is later
+// renamed or deleted.
+type OrderItem struct {
+	ID             uuid.UUID  `gorm:"type:uuid;primaryKey"`
+	OrderID        uuid.UUID  `gorm:"type:uuid;not null;index"`
+	ProductID      *uuid.UUID `gorm:"type:uuid"`
+	ProductName    string     `gorm:"not null"`
+	PriceTierID    *uuid.UUID `gorm:"type:uuid"`
+	UnitSymbol     string     `gorm:"not null"`
+	TierQuantity   float64    `gorm:"not null"`
+	Multiplier     int64      `gorm:"not null;default:1"`
+	UnitPriceCents int64      `gorm:"not null"`
+	TotalCents     int64      `gorm:"not null"`
+	CreatedAt      time.Time
+}
+
+func (OrderItem) TableName() string { return "order_items" }

backend/internal/modules/orders/repository.go

@@ -0,0 +1,85 @@
+package orders
+
+import (
+	"context"
+	"errors"
+
+	"github.com/google/uuid"
+	"gorm.io/gorm"
+)
+
+var ErrNotFound = errors.New("order not found")
+
+type Repository interface {
+	Create(ctx context.Context, order *Order, items []*OrderItem) error
+	FindByID(ctx context.Context, id uuid.UUID) (*Order, []*OrderItem, error)
+	List(ctx context.Context, status string) ([]*Order, error)
+	UpdateStatus(ctx context.Context, id uuid.UUID, status string) (*Order, error)
+}
+
+type gormRepository struct {
+	db *gorm.DB
+}
+
+func NewRepository(db *gorm.DB) Repository {
+	return &gormRepository{db: db}
+}
+
+func (r *gormRepository) Create(ctx context.Context, order *Order, items []*OrderItem) error {
+	return r.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
+		if err := tx.Create(order).Error; err != nil {
+			return err
+		}
+		for _, item := range items {
+			item.OrderID = order.ID
+		}
+		if len(items) > 0 {
+			if err := tx.Create(&items).Error; err != nil {
+				return err
+			}
+		}
+		return nil
+	})
+}
+
+func (r *gormRepository) FindByID(ctx context.Context, id uuid.UUID) (*Order, []*OrderItem, error) {
+	var order Order
+	if err := r.db.WithContext(ctx).Where("id = ?", id).First(&order).Error; err != nil {
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			return nil, nil, ErrNotFound
+		}
+		return nil, nil, err
+	}
+	var items []*OrderItem
+	if err := r.db.WithContext(ctx).Where("order_id = ?", id).Order("created_at asc").Find(&items).Error; err != nil {
+		return nil, nil, err
+	}
+	return &order, items, nil
+}
+
+func (r *gormRepository) List(ctx context.Context, status string) ([]*Order, error) {
+	q := r.db.WithContext(ctx).Order("created_at desc")
+	if status != "" {
+		q = q.Where("status = ?", status)
+	}
+	var list []*Order
+	if err := q.Find(&list).Error; err != nil {
+		return nil, err
+	}
+	return list, nil
+}
+
+func (r *gormRepository) UpdateStatus(ctx context.Context, id uuid.UUID, status string) (*Order, error) {
+	res := r.db.WithContext(ctx).Model(&Order{}).Where("id = ?", id).Update("status", status)
+	if res.Error != nil {
+		return nil, res.Error
+	}
+	if res.RowsAffected == 0 {
+		return nil, ErrNotFound
+	}
+	var order Order
+	if err := r.db.WithContext(ctx).Where("id = ?", id).First(&order).Error; err != nil {
+		return nil, err
+	}
+	return &order, nil
+}

backend/internal/modules/orders/routes.go

@@ -0,0 +1,17 @@
+package orders
+
+import "github.com/gin-gonic/gin"
+
+// RegisterPublicRoutes exposes order creation to any visitor, connected or
+// not (spec section 17-18). rateLimit throttles it to blunt spam/abuse
+// since no authentication gates this endpoint.
+func RegisterPublicRoutes(rg *gin.RouterGroup, h *Handler, rateLimit gin.HandlerFunc) {
+	rg.POST("/orders", rateLimit, h.Create)
+}
+
+func RegisterAdminRoutes(rg *gin.RouterGroup, h *Handler, requireAdmin gin.HandlerFunc) {
+	group := rg.Group("/admin/orders", requireAdmin)
+	group.GET("", h.ListAdmin)
+	group.GET("/:id", h.GetAdmin)
+	group.PATCH("/:id/status", h.UpdateStatus)
+}

backend/internal/modules/orders/service.go

@@ -0,0 +1,171 @@
+package orders
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+
+	"github.com/google/uuid"
+
+	"backend/internal/modules/pricing"
+	"backend/internal/modules/products"
+	"backend/internal/modules/units"
+)
+
+var (
+	ErrEmptyOrder      = errors.New("order must contain at least one item")
+	ErrInvalidStatus   = errors.New("invalid order status")
+	ErrProductMismatch = errors.New("price tier does not belong to the requested product")
+)
+
+// The dependencies below are the minimal slices of other modules' services
+// this module needs, defined on the consumer side (Go idiom) so orders
+// never has to import their concrete handler/repository types.
+type ProductFinder interface {
+	Get(ctx context.Context, id uuid.UUID) (*products.Product, error)
+}
+
+type UnitFinder interface {
+	Get(ctx context.Context, id uuid.UUID) (*units.Unit, error)
+}
+
+type PriceResolver interface {
+	PriceForQuantity(ctx context.Context, tierID uuid.UUID, multiplier int64) (int64, *pricing.PriceTier, error)
+}
+
+// OrderNotifier is satisfied by the telegram module's Service (and, later,
+// any other notification channel) without orders ever depending on it
+// directly.
+type OrderNotifier interface {
+	NotifyNewOrder(ctx context.Context, summary string)
+	NotifyOrderStatusChange(ctx context.Context, summary string)
+}
+
+type Service struct {
+	repo     Repository
+	products ProductFinder
+	units    UnitFinder
+	prices   PriceResolver
+	notifier OrderNotifier
+}
+
+func NewService(repo Repository, products ProductFinder, units UnitFinder, prices PriceResolver, notifier OrderNotifier) *Service {
+	return &Service{repo: repo, products: products, units: units, prices: prices, notifier: notifier}
+}
+
+type ItemInput struct {
+	ProductID   uuid.UUID
+	PriceTierID uuid.UUID
+	Multiplier  int64
+}
+
+type CreateInput struct {
+	CustomerName  string
+	CustomerEmail string
+	CustomerPhone string
+	Notes         string
+	Items         []ItemInput
+}
+
+func (s *Service) Create(ctx context.Context, in CreateInput) (*Order, []*OrderItem, error) {
+	if len(in.Items) == 0 {
+		return nil, nil, ErrEmptyOrder
+	}
+
+	order := &Order{
+		ID:            uuid.New(),
+		CustomerName:  in.CustomerName,
+		CustomerEmail: in.CustomerEmail,
+		CustomerPhone: in.CustomerPhone,
+		Status:        StatusPending,
+		Notes:         in.Notes,
+	}
+
+	items := make([]*OrderItem, 0, len(in.Items))
+	var total int64
+
+	for _, in := range in.Items {
+		multiplier := in.Multiplier
+		if multiplier < 1 {
+			multiplier = 1
+		}
+
+		lineTotal, tier, err := s.prices.PriceForQuantity(ctx, in.PriceTierID, multiplier)
+		if err != nil {
+			return nil, nil, fmt.Errorf("resolve price tier %s: %w", in.PriceTierID, err)
+		}
+		if tier.ProductID != in.ProductID {
+			return nil, nil, ErrProductMismatch
+		}
+
+		product, err := s.products.Get(ctx, in.ProductID)
+		if err != nil {
+			return nil, nil, fmt.Errorf("resolve product %s: %w", in.ProductID, err)
+		}
+		unit, err := s.units.Get(ctx, tier.UnitID)
+		if err != nil {
+			return nil, nil, fmt.Errorf("resolve unit %s: %w", tier.UnitID, err)
+		}
+
+		items = append(items, &OrderItem{
+			ID:             uuid.New(),
+			ProductID:      &product.ID,
+			ProductName:    product.Name,
+			PriceTierID:    &tier.ID,
+			UnitSymbol:     unit.Symbol,
+			TierQuantity:   tier.Quantity,
+			Multiplier:     multiplier,
+			UnitPriceCents: tier.PriceCents,
+			TotalCents:     lineTotal,
+		})
+		total += lineTotal
+	}
+
+	order.TotalCents = total
+
+	if err := s.repo.Create(ctx, order, items); err != nil {
+		return nil, nil, err
+	}
+
+	s.notifier.NotifyNewOrder(context.Background(), summarizeNewOrder(order, items))
+
+	return order, items, nil
+}
+
+func (s *Service) Get(ctx context.Context, id uuid.UUID) (*Order, []*OrderItem, error) {
+	return s.repo.FindByID(ctx, id)
+}
+
+func (s *Service) List(ctx context.Context, status string) ([]*Order, error) {
+	return s.repo.List(ctx, status)
+}
+
+func (s *Service) UpdateStatus(ctx context.Context, id uuid.UUID, status string) (*Order, error) {
+	if !ValidStatuses[status] {
+		return nil, ErrInvalidStatus
+	}
+	order, err := s.repo.UpdateStatus(ctx, id, status)
+	if err != nil {
+		return nil, err
+	}
+	s.notifier.NotifyOrderStatusChange(context.Background(), fmt.Sprintf(
+		"Order %s status changed to %q (customer: %s)", order.ID, order.Status, order.CustomerName,
+	))
+	return order, nil
+}
+
+func summarizeNewOrder(order *Order, items []*OrderItem) string {
+	var b strings.Builder
+	fmt.Fprintf(&b, "New order from %s (%s)\n", order.CustomerName, order.CustomerEmail)
+	for _, item := range items {
+		fmt.Fprintf(&b, "- %dx %s (%.2f %s) = %.2f\n",
+			item.Multiplier, item.ProductName, item.TierQuantity, item.UnitSymbol, centsToUnits(item.TotalCents))
+	}
+	fmt.Fprintf(&b, "Total: %.2f", centsToUnits(order.TotalCents))
+	return b.String()
+}
+
+func centsToUnits(cents int64) float64 {
+	return float64(cents) / 100
+}

backend/internal/modules/pricing/handler.go

@@ -0,0 +1,128 @@
+package pricing
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+)
+
+type Handler struct {
+	service *Service
+}
+
+func NewHandler(service *Service) *Handler {
+	return &Handler{service: service}
+}
+
+type tierResponse struct {
+	ID         uuid.UUID `json:"id"`
+	ProductID  uuid.UUID `json:"product_id"`
+	UnitID     uuid.UUID `json:"unit_id"`
+	Quantity   float64   `json:"quantity"`
+	PriceCents int64     `json:"price_cents"`
+	Position   int       `json:"position"`
+}
+
+func toResponse(t *PriceTier) tierResponse {
+	return tierResponse{
+		ID:         t.ID,
+		ProductID:  t.ProductID,
+		UnitID:     t.UnitID,
+		Quantity:   t.Quantity,
+		PriceCents: t.PriceCents,
+		Position:   t.Position,
+	}
+}
+
+func (h *Handler) ListByProduct(c *gin.Context) {
+	productID, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid product id"})
+		return
+	}
+	list, err := h.service.ListByProduct(c.Request.Context(), productID)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to list price tiers"})
+		return
+	}
+	resp := make([]tierResponse, 0, len(list))
+	for _, t := range list {
+		resp = append(resp, toResponse(t))
+	}
+	c.JSON(http.StatusOK, gin.H{"price_tiers": resp})
+}
+
+type upsertRequest struct {
+	UnitID     uuid.UUID `json:"unit_id" binding:"required"`
+	Quantity   float64   `json:"quantity" binding:"required,gt=0"`
+	PriceCents int64     `json:"price_cents" binding:"gte=0"`
+	Position   int       `json:"position"`
+}
+
+func (h *Handler) Create(c *gin.Context) {
+	productID, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid product id"})
+		return
+	}
+	var req upsertRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	t, err := h.service.Create(c.Request.Context(), productID, req.UnitID, req.Quantity, req.PriceCents, req.Position)
+	if err != nil {
+		if errors.Is(err, ErrInvalidReference) {
+			c.JSON(http.StatusBadRequest, gin.H{"error": "product or unit does not exist"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to create price tier"})
+		return
+	}
+	c.JSON(http.StatusCreated, toResponse(t))
+}
+
+func (h *Handler) Update(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("tierId"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	var req upsertRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	t, err := h.service.Update(c.Request.Context(), id, req.UnitID, req.Quantity, req.PriceCents, req.Position)
+	if err != nil {
+		switch {
+		case errors.Is(err, ErrNotFound):
+			c.JSON(http.StatusNotFound, gin.H{"error": "price tier not found"})
+		case errors.Is(err, ErrInvalidReference):
+			c.JSON(http.StatusBadRequest, gin.H{"error": "product or unit does not exist"})
+		default:
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to update price tier"})
+		}
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(t))
+}
+
+func (h *Handler) Delete(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("tierId"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	if err := h.service.Delete(c.Request.Context(), id); err != nil {
+		if errors.Is(err, ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "price tier not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to delete price tier"})
+		return
+	}
+	c.Status(http.StatusNoContent)
+}

backend/internal/modules/pricing/model.go

@@ -0,0 +1,26 @@
+// Package pricing implements quantity-based pricing for products (spec
+// section 16): a product can have several price tiers, each pairing a
+// quantity with a unit (from the units module) and a price. Pricing logic
+// (computing an order line's total from a chosen tier) is centralized here
+// in the backend -- the frontend only ever displays tiers and sends back a
+// tier ID + multiplier; it never sends a price the backend has to trust.
+package pricing
+
+import (
+	"time"
+
+	"github.com/google/uuid"
+)
+
+type PriceTier struct {
+	ID         uuid.UUID `gorm:"type:uuid;primaryKey"`
+	ProductID  uuid.UUID `gorm:"type:uuid;not null;index"`
+	UnitID     uuid.UUID `gorm:"type:uuid;not null"`
+	Quantity   float64   `gorm:"not null"`
+	PriceCents int64     `gorm:"not null"`
+	Position   int       `gorm:"not null;default:0"`
+	CreatedAt  time.Time
+	UpdatedAt  time.Time
+}
+
+func (PriceTier) TableName() string { return "price_tiers" }

backend/internal/modules/pricing/repository.go

@@ -0,0 +1,86 @@
+package pricing
+
+import (
+	"context"
+	"errors"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgconn"
+	"gorm.io/gorm"
+)
+
+var (
+	ErrNotFound         = errors.New("price tier not found")
+	ErrInvalidReference = errors.New("product or unit does not exist")
+)
+
+type Repository interface {
+	Create(ctx context.Context, t *PriceTier) error
+	FindByID(ctx context.Context, id uuid.UUID) (*PriceTier, error)
+	ListByProduct(ctx context.Context, productID uuid.UUID) ([]*PriceTier, error)
+	Update(ctx context.Context, t *PriceTier) error
+	Delete(ctx context.Context, id uuid.UUID) error
+}
+
+type gormRepository struct {
+	db *gorm.DB
+}
+
+func NewRepository(db *gorm.DB) Repository {
+	return &gormRepository{db: db}
+}
+
+func (r *gormRepository) Create(ctx context.Context, t *PriceTier) error {
+	if err := r.db.WithContext(ctx).Create(t).Error; err != nil {
+		if isForeignKeyViolation(err) {
+			return ErrInvalidReference
+		}
+		return err
+	}
+	return nil
+}
+
+func (r *gormRepository) FindByID(ctx context.Context, id uuid.UUID) (*PriceTier, error) {
+	var t PriceTier
+	err := r.db.WithContext(ctx).Where("id = ?", id).First(&t).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &t, nil
+}
+
+func (r *gormRepository) ListByProduct(ctx context.Context, productID uuid.UUID) ([]*PriceTier, error) {
+	var list []*PriceTier
+	err := r.db.WithContext(ctx).Where("product_id = ?", productID).Order("position asc, quantity asc").Find(&list).Error
+	if err != nil {
+		return nil, err
+	}
+	return list, nil
+}
+
+func (r *gormRepository) Update(ctx context.Context, t *PriceTier) error {
+	err := r.db.WithContext(ctx).Save(t).Error
+	if isForeignKeyViolation(err) {
+		return ErrInvalidReference
+	}
+	return err
+}
+
+func (r *gormRepository) Delete(ctx context.Context, id uuid.UUID) error {
+	res := r.db.WithContext(ctx).Delete(&PriceTier{}, "id = ?", id)
+	if res.Error != nil {
+		return res.Error
+	}
+	if res.RowsAffected == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
+func isForeignKeyViolation(err error) bool {
+	var pgErr *pgconn.PgError
+	return errors.As(err, &pgErr) && pgErr.Code == "23503"
+}

backend/internal/modules/pricing/routes.go

@@ -0,0 +1,24 @@
+package pricing
+
+import "github.com/gin-gonic/gin"
+
+// RegisterAdminRoutes nests price-tier management under a product, e.g.
+// PUT /api/admin/products/:id/price-tiers/:tierId, so tiers are always
+// managed in the context of the product they belong to.
+func RegisterAdminRoutes(rg *gin.RouterGroup, h *Handler, requireAdmin gin.HandlerFunc) {
+	group := rg.Group("/admin/products/:id/price-tiers", requireAdmin)
+	group.GET("", h.ListByProduct)
+	group.POST("", h.Create)
+	group.PUT("/:tierId", h.Update)
+	group.DELETE("/:tierId", h.Delete)
+}
+
+// RegisterPublicRoutes exposes read-only tiers so the storefront can render
+// the available quantity/price options for a product. Kept as its own
+// top-level path (rather than nested under /products/:slug) because the
+// products module's public detail route uses a :slug wildcard at that same
+// position -- gin does not allow two different wildcard names at the same
+// path segment.
+func RegisterPublicRoutes(rg *gin.RouterGroup, h *Handler) {
+	rg.GET("/price-tiers/by-product/:id", h.ListByProduct)
+}

backend/internal/modules/pricing/service.go

@@ -0,0 +1,72 @@
+package pricing
+
+import (
+	"context"
+
+	"github.com/google/uuid"
+)
+
+type Service struct {
+	repo Repository
+}
+
+func NewService(repo Repository) *Service {
+	return &Service{repo: repo}
+}
+
+func (s *Service) ListByProduct(ctx context.Context, productID uuid.UUID) ([]*PriceTier, error) {
+	return s.repo.ListByProduct(ctx, productID)
+}
+
+func (s *Service) Get(ctx context.Context, id uuid.UUID) (*PriceTier, error) {
+	return s.repo.FindByID(ctx, id)
+}
+
+func (s *Service) Create(ctx context.Context, productID, unitID uuid.UUID, quantity float64, priceCents int64, position int) (*PriceTier, error) {
+	t := &PriceTier{
+		ID:         uuid.New(),
+		ProductID:  productID,
+		UnitID:     unitID,
+		Quantity:   quantity,
+		PriceCents: priceCents,
+		Position:   position,
+	}
+	if err := s.repo.Create(ctx, t); err != nil {
+		return nil, err
+	}
+	return t, nil
+}
+
+func (s *Service) Update(ctx context.Context, id uuid.UUID, unitID uuid.UUID, quantity float64, priceCents int64, position int) (*PriceTier, error) {
+	t, err := s.repo.FindByID(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	t.UnitID = unitID
+	t.Quantity = quantity
+	t.PriceCents = priceCents
+	t.Position = position
+	if err := s.repo.Update(ctx, t); err != nil {
+		return nil, err
+	}
+	return t, nil
+}
+
+func (s *Service) Delete(ctx context.Context, id uuid.UUID) error {
+	return s.repo.Delete(ctx, id)
+}
+
+// PriceForQuantity is the centralized pricing calculation used by the
+// orders module: given a chosen tier and how many of that tier package the
+// customer wants, it returns the authoritative total in cents. The
+// frontend never gets to supply a price directly.
+func (s *Service) PriceForQuantity(ctx context.Context, tierID uuid.UUID, multiplier int64) (totalCents int64, tier *PriceTier, err error) {
+	t, err := s.repo.FindByID(ctx, tierID)
+	if err != nil {
+		return 0, nil, err
+	}
+	if multiplier < 1 {
+		multiplier = 1
+	}
+	return t.PriceCents * multiplier, t, nil
+}

backend/internal/modules/products/handler.go

@@ -0,0 +1,303 @@
+package products
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+)
+
+type Handler struct {
+	service *Service
+}
+
+func NewHandler(service *Service) *Handler {
+	return &Handler{service: service}
+}
+
+type galleryItemResponse struct {
+	MediaID  uuid.UUID `json:"media_id"`
+	Position int       `json:"position"`
+}
+
+type productResponse struct {
+	ID               uuid.UUID  `json:"id"`
+	CategoryID       *uuid.UUID `json:"category_id,omitempty"`
+	Name             string     `json:"name"`
+	Slug             string     `json:"slug"`
+	ShortDescription string     `json:"short_description"`
+	Description      string     `json:"description"`
+	IsActive         bool       `json:"is_active"`
+	IsFeatured       bool       `json:"is_featured"`
+	PrimaryMediaID   *uuid.UUID `json:"primary_media_id,omitempty"`
+	Position         int        `json:"position"`
+}
+
+func toResponse(p *Product) productResponse {
+	return productResponse{
+		ID:               p.ID,
+		CategoryID:       p.CategoryID,
+		Name:             p.Name,
+		Slug:             p.Slug,
+		ShortDescription: p.ShortDescription,
+		Description:      p.Description,
+		IsActive:         p.IsActive,
+		IsFeatured:       p.IsFeatured,
+		PrimaryMediaID:   p.PrimaryMediaID,
+		Position:         p.Position,
+	}
+}
+
+func parseCategoryFilter(c *gin.Context) *uuid.UUID {
+	raw := c.Query("category_id")
+	if raw == "" {
+		return nil
+	}
+	id, err := uuid.Parse(raw)
+	if err != nil {
+		return nil
+	}
+	return &id
+}
+
+func (h *Handler) ListAdmin(c *gin.Context) {
+	list, err := h.service.List(c.Request.Context(), false, parseCategoryFilter(c))
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to list products"})
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"products": toResponseList(list)})
+}
+
+func (h *Handler) ListPublic(c *gin.Context) {
+	list, err := h.service.List(c.Request.Context(), true, parseCategoryFilter(c))
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to list products"})
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"products": toResponseList(list)})
+}
+
+func toResponseList(list []*Product) []productResponse {
+	resp := make([]productResponse, 0, len(list))
+	for _, p := range list {
+		resp = append(resp, toResponse(p))
+	}
+	return resp
+}
+
+func (h *Handler) GetAdmin(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	p, err := h.service.Get(c.Request.Context(), id)
+	if err != nil {
+		h.respondGetError(c, err)
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(p))
+}
+
+func (h *Handler) GetPublicBySlug(c *gin.Context) {
+	p, err := h.service.GetBySlug(c.Request.Context(), c.Param("slug"))
+	if err != nil {
+		h.respondGetError(c, err)
+		return
+	}
+	if !p.IsActive {
+		c.JSON(http.StatusNotFound, gin.H{"error": "product not found"})
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(p))
+}
+
+func (h *Handler) respondGetError(c *gin.Context, err error) {
+	if errors.Is(err, ErrNotFound) {
+		c.JSON(http.StatusNotFound, gin.H{"error": "product not found"})
+		return
+	}
+	c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to load product"})
+}
+
+type upsertRequest struct {
+	CategoryID       *uuid.UUID `json:"category_id"`
+	Name             string     `json:"name" binding:"required"`
+	Slug             string     `json:"slug" binding:"required"`
+	ShortDescription string     `json:"short_description"`
+	Description      string     `json:"description"`
+	IsActive         bool       `json:"is_active"`
+	IsFeatured       bool       `json:"is_featured"`
+	PrimaryMediaID   *uuid.UUID `json:"primary_media_id"`
+	Position         int        `json:"position"`
+}
+
+func (req upsertRequest) toInput() UpsertInput {
+	return UpsertInput{
+		CategoryID:       req.CategoryID,
+		Name:             req.Name,
+		Slug:             req.Slug,
+		ShortDescription: req.ShortDescription,
+		Description:      req.Description,
+		IsActive:         req.IsActive,
+		IsFeatured:       req.IsFeatured,
+		PrimaryMediaID:   req.PrimaryMediaID,
+		Position:         req.Position,
+	}
+}
+
+func (h *Handler) Create(c *gin.Context) {
+	var req upsertRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	p, err := h.service.Create(c.Request.Context(), req.toInput())
+	if err != nil {
+		if errors.Is(err, ErrSlugTaken) {
+			c.JSON(http.StatusConflict, gin.H{"error": "slug already in use"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to create product"})
+		return
+	}
+	c.JSON(http.StatusCreated, toResponse(p))
+}
+
+func (h *Handler) Update(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	var req upsertRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	p, err := h.service.Update(c.Request.Context(), id, req.toInput())
+	if err != nil {
+		switch {
+		case errors.Is(err, ErrNotFound):
+			c.JSON(http.StatusNotFound, gin.H{"error": "product not found"})
+		case errors.Is(err, ErrSlugTaken):
+			c.JSON(http.StatusConflict, gin.H{"error": "slug already in use"})
+		default:
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to update product"})
+		}
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(p))
+}
+
+type updatePositionRequest struct {
+	Position int `json:"position"`
+}
+
+// UpdatePosition lets the admin reorder the catalog display order (e.g.
+// move up/move down in the admin list) without resending the whole
+// product payload.
+func (h *Handler) UpdatePosition(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	var req updatePositionRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	p, err := h.service.UpdatePosition(c.Request.Context(), id, req.Position)
+	if err != nil {
+		if errors.Is(err, ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "product not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to update position"})
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(p))
+}
+
+func (h *Handler) Delete(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	if err := h.service.Delete(c.Request.Context(), id); err != nil {
+		if errors.Is(err, ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "product not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to delete product"})
+		return
+	}
+	c.Status(http.StatusNoContent)
+}
+
+type addGalleryRequest struct {
+	MediaID  uuid.UUID `json:"media_id" binding:"required"`
+	Position int       `json:"position"`
+}
+
+func (h *Handler) AddGalleryItem(c *gin.Context) {
+	productID, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	var req addGalleryRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	if err := h.service.AddGalleryItem(c.Request.Context(), productID, req.MediaID, req.Position); err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to attach media"})
+		return
+	}
+	c.Status(http.StatusCreated)
+}
+
+func (h *Handler) RemoveGalleryItem(c *gin.Context) {
+	productID, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	mediaID, err := uuid.Parse(c.Param("mediaId"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid media id"})
+		return
+	}
+	if err := h.service.RemoveGalleryItem(c.Request.Context(), productID, mediaID); err != nil {
+		if errors.Is(err, ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "gallery item not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to detach media"})
+		return
+	}
+	c.Status(http.StatusNoContent)
+}
+
+func (h *Handler) ListGallery(c *gin.Context) {
+	productID, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	items, err := h.service.ListGallery(c.Request.Context(), productID)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to list gallery"})
+		return
+	}
+	resp := make([]galleryItemResponse, 0, len(items))
+	for _, item := range items {
+		resp = append(resp, galleryItemResponse{MediaID: item.MediaID, Position: item.Position})
+	}
+	c.JSON(http.StatusOK, gin.H{"gallery": resp})
+}

backend/internal/modules/products/model.go

@@ -0,0 +1,41 @@
+// Package products owns the product catalog entity itself (identity,
+// description, category, media). Quantity-based pricing lives in the
+// pricing module, which references products by ID -- keeping "what a
+// product is" separate from "how it's priced", per spec section 13/16.
+package products
+
+import (
+	"time"
+
+	"github.com/google/uuid"
+)
+
+type Product struct {
+	ID               uuid.UUID  `gorm:"type:uuid;primaryKey"`
+	CategoryID       *uuid.UUID `gorm:"type:uuid"`
+	Name             string     `gorm:"not null"`
+	Slug             string     `gorm:"uniqueIndex;not null"`
+	ShortDescription string     `gorm:"not null;default:''"`
+	Description      string     `gorm:"not null;default:''"`
+	IsActive         bool       `gorm:"not null;default:true"`
+	IsFeatured       bool       `gorm:"not null;default:false"`
+	PrimaryMediaID   *uuid.UUID `gorm:"type:uuid"`
+	Position         int        `gorm:"not null;default:0"`
+	CreatedAt        time.Time
+	UpdatedAt        time.Time
+}
+
+func (Product) TableName() string { return "products" }
+
+// GalleryItem attaches a media item to a product's gallery, ordered by
+// Position. A product's primary image (PrimaryMediaID) is separate from
+// the gallery so it can be picked from unrelated media too.
+type GalleryItem struct {
+	ID        uuid.UUID `gorm:"type:uuid;primaryKey"`
+	ProductID uuid.UUID `gorm:"type:uuid;not null;index"`
+	MediaID   uuid.UUID `gorm:"type:uuid;not null"`
+	Position  int       `gorm:"not null;default:0"`
+	CreatedAt time.Time
+}
+
+func (GalleryItem) TableName() string { return "product_media" }

backend/internal/modules/products/repository.go

@@ -0,0 +1,132 @@
+package products
+
+import (
+	"context"
+	"errors"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgconn"
+	"gorm.io/gorm"
+)
+
+var (
+	ErrNotFound  = errors.New("product not found")
+	ErrSlugTaken = errors.New("slug already in use")
+)
+
+type Repository interface {
+	Create(ctx context.Context, p *Product) error
+	FindByID(ctx context.Context, id uuid.UUID) (*Product, error)
+	FindBySlug(ctx context.Context, slug string) (*Product, error)
+	List(ctx context.Context, activeOnly bool, categoryID *uuid.UUID) ([]*Product, error)
+	Update(ctx context.Context, p *Product) error
+	Delete(ctx context.Context, id uuid.UUID) error
+
+	AddGalleryItem(ctx context.Context, item *GalleryItem) error
+	RemoveGalleryItem(ctx context.Context, productID, mediaID uuid.UUID) error
+	ListGallery(ctx context.Context, productID uuid.UUID) ([]*GalleryItem, error)
+}
+
+type gormRepository struct {
+	db *gorm.DB
+}
+
+func NewRepository(db *gorm.DB) Repository {
+	return &gormRepository{db: db}
+}
+
+func (r *gormRepository) Create(ctx context.Context, p *Product) error {
+	if err := r.db.WithContext(ctx).Create(p).Error; err != nil {
+		if isUniqueViolation(err) {
+			return ErrSlugTaken
+		}
+		return err
+	}
+	return nil
+}
+
+func (r *gormRepository) FindByID(ctx context.Context, id uuid.UUID) (*Product, error) {
+	var p Product
+	err := r.db.WithContext(ctx).Where("id = ?", id).First(&p).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &p, nil
+}
+
+func (r *gormRepository) FindBySlug(ctx context.Context, slug string) (*Product, error) {
+	var p Product
+	err := r.db.WithContext(ctx).Where("slug = ?", slug).First(&p).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &p, nil
+}
+
+func (r *gormRepository) List(ctx context.Context, activeOnly bool, categoryID *uuid.UUID) ([]*Product, error) {
+	q := r.db.WithContext(ctx).Order("position asc, created_at desc")
+	if activeOnly {
+		q = q.Where("is_active = ?", true)
+	}
+	if categoryID != nil {
+		q = q.Where("category_id = ?", *categoryID)
+	}
+	var list []*Product
+	if err := q.Find(&list).Error; err != nil {
+		return nil, err
+	}
+	return list, nil
+}
+
+func (r *gormRepository) Update(ctx context.Context, p *Product) error {
+	err := r.db.WithContext(ctx).Save(p).Error
+	if isUniqueViolation(err) {
+		return ErrSlugTaken
+	}
+	return err
+}
+
+func (r *gormRepository) Delete(ctx context.Context, id uuid.UUID) error {
+	res := r.db.WithContext(ctx).Delete(&Product{}, "id = ?", id)
+	if res.Error != nil {
+		return res.Error
+	}
+	if res.RowsAffected == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
+func (r *gormRepository) AddGalleryItem(ctx context.Context, item *GalleryItem) error {
+	return r.db.WithContext(ctx).Create(item).Error
+}
+
+func (r *gormRepository) RemoveGalleryItem(ctx context.Context, productID, mediaID uuid.UUID) error {
+	res := r.db.WithContext(ctx).Delete(&GalleryItem{}, "product_id = ? AND media_id = ?", productID, mediaID)
+	if res.Error != nil {
+		return res.Error
+	}
+	if res.RowsAffected == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
+func (r *gormRepository) ListGallery(ctx context.Context, productID uuid.UUID) ([]*GalleryItem, error) {
+	var list []*GalleryItem
+	if err := r.db.WithContext(ctx).Where("product_id = ?", productID).Order("position asc").Find(&list).Error; err != nil {
+		return nil, err
+	}
+	return list, nil
+}
+
+func isUniqueViolation(err error) bool {
+	var pgErr *pgconn.PgError
+	return errors.As(err, &pgErr) && pgErr.Code == "23505"
+}

backend/internal/modules/products/routes.go

@@ -0,0 +1,24 @@
+package products
+
+import "github.com/gin-gonic/gin"
+
+func RegisterAdminRoutes(rg *gin.RouterGroup, h *Handler, requireAdmin gin.HandlerFunc) {
+	group := rg.Group("/admin/products", requireAdmin)
+	group.GET("", h.ListAdmin)
+	group.POST("", h.Create)
+	group.GET("/:id", h.GetAdmin)
+	group.PUT("/:id", h.Update)
+	group.PATCH("/:id/position", h.UpdatePosition)
+	group.DELETE("/:id", h.Delete)
+
+	group.GET("/:id/gallery", h.ListGallery)
+	group.POST("/:id/gallery", h.AddGalleryItem)
+	group.DELETE("/:id/gallery/:mediaId", h.RemoveGalleryItem)
+}
+
+// RegisterPublicRoutes exposes the read-only, active-only product catalog
+// used by the storefront (site vitrine / boutique).
+func RegisterPublicRoutes(rg *gin.RouterGroup, h *Handler) {
+	rg.GET("/products", h.ListPublic)
+	rg.GET("/products/:slug", h.GetPublicBySlug)
+}

backend/internal/modules/products/service.go

@@ -0,0 +1,113 @@
+package products
+
+import (
+	"context"
+
+	"github.com/google/uuid"
+)
+
+type Service struct {
+	repo Repository
+}
+
+func NewService(repo Repository) *Service {
+	return &Service{repo: repo}
+}
+
+func (s *Service) List(ctx context.Context, activeOnly bool, categoryID *uuid.UUID) ([]*Product, error) {
+	return s.repo.List(ctx, activeOnly, categoryID)
+}
+
+func (s *Service) Get(ctx context.Context, id uuid.UUID) (*Product, error) {
+	return s.repo.FindByID(ctx, id)
+}
+
+func (s *Service) GetBySlug(ctx context.Context, slug string) (*Product, error) {
+	return s.repo.FindBySlug(ctx, slug)
+}
+
+type UpsertInput struct {
+	CategoryID       *uuid.UUID
+	Name             string
+	Slug             string
+	ShortDescription string
+	Description      string
+	IsActive         bool
+	IsFeatured       bool
+	PrimaryMediaID   *uuid.UUID
+	Position         int
+}
+
+func (s *Service) Create(ctx context.Context, in UpsertInput) (*Product, error) {
+	p := &Product{
+		ID:               uuid.New(),
+		CategoryID:       in.CategoryID,
+		Name:             in.Name,
+		Slug:             in.Slug,
+		ShortDescription: in.ShortDescription,
+		Description:      in.Description,
+		IsActive:         in.IsActive,
+		IsFeatured:       in.IsFeatured,
+		PrimaryMediaID:   in.PrimaryMediaID,
+		Position:         in.Position,
+	}
+	if err := s.repo.Create(ctx, p); err != nil {
+		return nil, err
+	}
+	return p, nil
+}
+
+func (s *Service) Update(ctx context.Context, id uuid.UUID, in UpsertInput) (*Product, error) {
+	p, err := s.repo.FindByID(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	p.CategoryID = in.CategoryID
+	p.Name = in.Name
+	p.Slug = in.Slug
+	p.ShortDescription = in.ShortDescription
+	p.Description = in.Description
+	p.IsActive = in.IsActive
+	p.IsFeatured = in.IsFeatured
+	p.PrimaryMediaID = in.PrimaryMediaID
+	p.Position = in.Position
+	if err := s.repo.Update(ctx, p); err != nil {
+		return nil, err
+	}
+	return p, nil
+}
+
+func (s *Service) Delete(ctx context.Context, id uuid.UUID) error {
+	return s.repo.Delete(ctx, id)
+}
+
+// UpdatePosition lets the admin reorder the catalog display order without
+// resending the full product payload.
+func (s *Service) UpdatePosition(ctx context.Context, id uuid.UUID, position int) (*Product, error) {
+	p, err := s.repo.FindByID(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	p.Position = position
+	if err := s.repo.Update(ctx, p); err != nil {
+		return nil, err
+	}
+	return p, nil
+}
+
+func (s *Service) AddGalleryItem(ctx context.Context, productID, mediaID uuid.UUID, position int) error {
+	return s.repo.AddGalleryItem(ctx, &GalleryItem{
+		ID:        uuid.New(),
+		ProductID: productID,
+		MediaID:   mediaID,
+		Position:  position,
+	})
+}
+
+func (s *Service) RemoveGalleryItem(ctx context.Context, productID, mediaID uuid.UUID) error {
+	return s.repo.RemoveGalleryItem(ctx, productID, mediaID)
+}
+
+func (s *Service) ListGallery(ctx context.Context, productID uuid.UUID) ([]*GalleryItem, error) {
+	return s.repo.ListGallery(ctx, productID)
+}

backend/internal/modules/site/handler.go

@@ -0,0 +1,62 @@
+package site
+
+import (
+	"net/http"
+	"regexp"
+
+	"github.com/gin-gonic/gin"
+)
+
+var slugPattern = regexp.MustCompile(`^[a-z0-9]+(-[a-z0-9]+)*$`)
+
+type Handler struct {
+	service *Service
+}
+
+func NewHandler(service *Service) *Handler {
+	return &Handler{service: service}
+}
+
+type settingsResponse struct {
+	Name        string `json:"name"`
+	Description string `json:"description"`
+	Slug        string `json:"slug"`
+}
+
+func toResponse(s *Settings) settingsResponse {
+	return settingsResponse{Name: s.Name, Description: s.Description, Slug: s.Slug}
+}
+
+func (h *Handler) Get(c *gin.Context) {
+	settings, err := h.service.Get(c.Request.Context())
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to load site settings"})
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(settings))
+}
+
+type updateRequest struct {
+	Name        string `json:"name" binding:"required"`
+	Description string `json:"description"`
+	Slug        string `json:"slug" binding:"required"`
+}
+
+func (h *Handler) Update(c *gin.Context) {
+	var req updateRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	if !slugPattern.MatchString(req.Slug) {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "slug must be lowercase letters, digits and hyphens only"})
+		return
+	}
+
+	settings, err := h.service.Update(c.Request.Context(), req.Name, req.Description, req.Slug)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to update site settings"})
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(settings))
+}

backend/internal/modules/site/model.go

@@ -0,0 +1,19 @@
+// Package site owns the minimal, config-driven site identity (name,
+// description, slug). It is the proof of the "code defines capabilities,
+// admin defines content" pattern: future modules (appearance, menu, pages,
+// ...) will follow this same shape (single-row or keyed settings table +
+// admin-only read/write endpoints).
+package site
+
+import "time"
+
+type Settings struct {
+	ID          int16 `gorm:"primaryKey"`
+	Name        string
+	Description string
+	Slug        string
+	CreatedAt   time.Time
+	UpdatedAt   time.Time
+}
+
+func (Settings) TableName() string { return "site_settings" }

backend/internal/modules/site/repository.go

@@ -0,0 +1,37 @@
+package site
+
+import (
+	"context"
+
+	"gorm.io/gorm"
+)
+
+type Repository interface {
+	Get(ctx context.Context) (*Settings, error)
+	Update(ctx context.Context, s *Settings) error
+}
+
+type gormRepository struct {
+	db *gorm.DB
+}
+
+func NewRepository(db *gorm.DB) Repository {
+	return &gormRepository{db: db}
+}
+
+func (r *gormRepository) Get(ctx context.Context) (*Settings, error) {
+	var s Settings
+	if err := r.db.WithContext(ctx).First(&s, "id = 1").Error; err != nil {
+		return nil, err
+	}
+	return &s, nil
+}
+
+func (r *gormRepository) Update(ctx context.Context, s *Settings) error {
+	s.ID = 1
+	return r.db.WithContext(ctx).Model(&Settings{}).Where("id = 1").Updates(map[string]any{
+		"name":        s.Name,
+		"description": s.Description,
+		"slug":        s.Slug,
+	}).Error
+}

backend/internal/modules/site/routes.go

@@ -0,0 +1,9 @@
+package site
+
+import "github.com/gin-gonic/gin"
+
+func RegisterRoutes(rg *gin.RouterGroup, h *Handler, requireAdmin gin.HandlerFunc) {
+	group := rg.Group("/admin/site-settings")
+	group.GET("", h.Get)
+	group.PUT("", requireAdmin, h.Update)
+}

backend/internal/modules/site/service.go

@@ -0,0 +1,23 @@
+package site
+
+import "context"
+
+type Service struct {
+	repo Repository
+}
+
+func NewService(repo Repository) *Service {
+	return &Service{repo: repo}
+}
+
+func (s *Service) Get(ctx context.Context) (*Settings, error) {
+	return s.repo.Get(ctx)
+}
+
+func (s *Service) Update(ctx context.Context, name, description, slug string) (*Settings, error) {
+	settings := &Settings{Name: name, Description: description, Slug: slug}
+	if err := s.repo.Update(ctx, settings); err != nil {
+		return nil, err
+	}
+	return s.repo.Get(ctx)
+}

backend/internal/modules/telegram/handler.go

@@ -0,0 +1,74 @@
+package telegram
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+type Handler struct {
+	service *Service
+}
+
+func NewHandler(service *Service) *Handler {
+	return &Handler{service: service}
+}
+
+// settingsResponse never includes the raw bot token (spec section 32: secrets
+// must never be exposed to the frontend) -- only whether one is configured.
+type settingsResponse struct {
+	Enabled            bool   `json:"enabled"`
+	BotTokenConfigured bool   `json:"bot_token_configured"`
+	ChatID             string `json:"chat_id"`
+	NotifyNewOrder     bool   `json:"notify_new_order"`
+	NotifyStatusChange bool   `json:"notify_status_change"`
+}
+
+func toResponse(s *Settings) settingsResponse {
+	return settingsResponse{
+		Enabled:            s.Enabled,
+		BotTokenConfigured: s.BotToken != "",
+		ChatID:             s.ChatID,
+		NotifyNewOrder:     s.NotifyNewOrder,
+		NotifyStatusChange: s.NotifyStatusChange,
+	}
+}
+
+func (h *Handler) Get(c *gin.Context) {
+	settings, err := h.service.Get(c.Request.Context())
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to load telegram settings"})
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(settings))
+}
+
+type updateRequest struct {
+	Enabled            bool   `json:"enabled"`
+	BotToken           string `json:"bot_token"`
+	ChatID             string `json:"chat_id" binding:"required_if=Enabled true"`
+	NotifyNewOrder     bool   `json:"notify_new_order"`
+	NotifyStatusChange bool   `json:"notify_status_change"`
+}
+
+func (h *Handler) Update(c *gin.Context) {
+	var req updateRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	settings, err := h.service.Update(c.Request.Context(), req.Enabled, req.BotToken, req.ChatID, req.NotifyNewOrder, req.NotifyStatusChange)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to update telegram settings"})
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(settings))
+}
+
+func (h *Handler) Test(c *gin.Context) {
+	if err := h.service.SendTestMessage(c.Request.Context()); err != nil {
+		c.JSON(http.StatusBadGateway, gin.H{"error": err.Error()})
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"message": "test notification sent"})
+}

backend/internal/modules/telegram/model.go

@@ -0,0 +1,22 @@
+// Package telegram is the notifications module (spec section 20): the
+// admin configures a bot token + chat id and toggles which events trigger a
+// message. It is a pluggable notifier -- other modules (orders) depend on
+// the small OrderNotifier interface it satisfies, never on Telegram
+// directly, so a future module (email, WhatsApp, ...) can be swapped in the
+// same way.
+package telegram
+
+import "time"
+
+type Settings struct {
+	ID                 int16 `gorm:"primaryKey"`
+	Enabled            bool
+	BotToken           string
+	ChatID             string
+	NotifyNewOrder     bool
+	NotifyStatusChange bool
+	CreatedAt          time.Time
+	UpdatedAt          time.Time
+}
+
+func (Settings) TableName() string { return "telegram_settings" }

backend/internal/modules/telegram/repository.go

@@ -0,0 +1,44 @@
+package telegram
+
+import (
+	"context"
+
+	"gorm.io/gorm"
+)
+
+type Repository interface {
+	Get(ctx context.Context) (*Settings, error)
+	Update(ctx context.Context, s *Settings) error
+}
+
+type gormRepository struct {
+	db *gorm.DB
+}
+
+func NewRepository(db *gorm.DB) Repository {
+	return &gormRepository{db: db}
+}
+
+func (r *gormRepository) Get(ctx context.Context) (*Settings, error) {
+	var s Settings
+	if err := r.db.WithContext(ctx).First(&s, "id = 1").Error; err != nil {
+		return nil, err
+	}
+	return &s, nil
+}
+
+func (r *gormRepository) Update(ctx context.Context, s *Settings) error {
+	s.ID = 1
+	updates := map[string]any{
+		"enabled":              s.Enabled,
+		"chat_id":              s.ChatID,
+		"notify_new_order":     s.NotifyNewOrder,
+		"notify_status_change": s.NotifyStatusChange,
+	}
+	// bot_token is only overwritten when explicitly provided (see service.go):
+	// a blank value in the update request means "keep the existing secret".
+	if s.BotToken != "" {
+		updates["bot_token"] = s.BotToken
+	}
+	return r.db.WithContext(ctx).Model(&Settings{}).Where("id = 1").Updates(updates).Error
+}

backend/internal/modules/telegram/routes.go

@@ -0,0 +1,10 @@
+package telegram
+
+import "github.com/gin-gonic/gin"
+
+func RegisterAdminRoutes(rg *gin.RouterGroup, h *Handler, requireAdmin gin.HandlerFunc) {
+	group := rg.Group("/admin/notifications/telegram", requireAdmin)
+	group.GET("", h.Get)
+	group.PUT("", h.Update)
+	group.POST("/test", h.Test)
+}

backend/internal/modules/telegram/sender.go

@@ -0,0 +1,55 @@
+package telegram
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+)
+
+// Sender abstracts the actual Telegram Bot API call so the service layer
+// can be unit-tested without making real network requests.
+type Sender interface {
+	Send(ctx context.Context, botToken, chatID, text string) error
+}
+
+type httpSender struct {
+	client *http.Client
+}
+
+func NewHTTPSender() Sender {
+	return &httpSender{client: &http.Client{Timeout: 10 * time.Second}}
+}
+
+func (s *httpSender) Send(ctx context.Context, botToken, chatID, text string) error {
+	if botToken == "" || chatID == "" {
+		return fmt.Errorf("telegram bot token and chat id must be configured")
+	}
+
+	endpoint := fmt.Sprintf("https://api.telegram.org/bot%s/sendMessage", botToken)
+	form := url.Values{
+		"chat_id": {chatID},
+		"text":    {text},
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, strings.NewReader(form.Encode()))
+	if err != nil {
+		return fmt.Errorf("build telegram request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+	resp, err := s.client.Do(req)
+	if err != nil {
+		return fmt.Errorf("call telegram api: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode >= 300 {
+		body, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
+		return fmt.Errorf("telegram api returned status %d: %s", resp.StatusCode, string(body))
+	}
+	return nil
+}

backend/internal/modules/telegram/service.go

@@ -0,0 +1,75 @@
+package telegram
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+)
+
+type Service struct {
+	repo   Repository
+	sender Sender
+	logger *slog.Logger
+}
+
+func NewService(repo Repository, sender Sender, logger *slog.Logger) *Service {
+	return &Service{repo: repo, sender: sender, logger: logger}
+}
+
+func (s *Service) Get(ctx context.Context) (*Settings, error) {
+	return s.repo.Get(ctx)
+}
+
+// Update persists the settings. botToken == "" means "leave the currently
+// stored token untouched" -- the admin never has to re-type the secret just
+// to flip a checkbox, and the API never has to echo it back.
+func (s *Service) Update(ctx context.Context, enabled bool, botToken, chatID string, notifyNewOrder, notifyStatusChange bool) (*Settings, error) {
+	settings := &Settings{
+		Enabled:            enabled,
+		BotToken:           botToken,
+		ChatID:             chatID,
+		NotifyNewOrder:     notifyNewOrder,
+		NotifyStatusChange: notifyStatusChange,
+	}
+	if err := s.repo.Update(ctx, settings); err != nil {
+		return nil, err
+	}
+	return s.repo.Get(ctx)
+}
+
+func (s *Service) SendTestMessage(ctx context.Context) error {
+	settings, err := s.repo.Get(ctx)
+	if err != nil {
+		return err
+	}
+	if settings.BotToken == "" || settings.ChatID == "" {
+		return fmt.Errorf("bot token and chat id must be configured before testing")
+	}
+	return s.sender.Send(ctx, settings.BotToken, settings.ChatID, "Test notification: your Telegram integration is working.")
+}
+
+// NotifyNewOrder implements orders.OrderNotifier. It never returns an error
+// to the caller: a broken/misconfigured Telegram integration must not
+// prevent a customer's order from being created, so failures are only
+// logged.
+func (s *Service) NotifyNewOrder(ctx context.Context, summary string) {
+	s.notify(ctx, func(st *Settings) bool { return st.NotifyNewOrder }, summary)
+}
+
+func (s *Service) NotifyOrderStatusChange(ctx context.Context, summary string) {
+	s.notify(ctx, func(st *Settings) bool { return st.NotifyStatusChange }, summary)
+}
+
+func (s *Service) notify(ctx context.Context, shouldSend func(*Settings) bool, text string) {
+	settings, err := s.repo.Get(ctx)
+	if err != nil {
+		s.logger.Error("telegram: failed to load settings", "error", err)
+		return
+	}
+	if !settings.Enabled || !shouldSend(settings) {
+		return
+	}
+	if err := s.sender.Send(ctx, settings.BotToken, settings.ChatID, text); err != nil {
+		s.logger.Error("telegram: failed to send notification", "error", err)
+	}
+}

backend/internal/modules/units/handler.go

@@ -0,0 +1,109 @@
+package units
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+)
+
+type Handler struct {
+	service *Service
+}
+
+func NewHandler(service *Service) *Handler {
+	return &Handler{service: service}
+}
+
+type unitResponse struct {
+	ID     uuid.UUID `json:"id"`
+	Name   string    `json:"name"`
+	Symbol string    `json:"symbol"`
+}
+
+func toResponse(u *Unit) unitResponse {
+	return unitResponse{ID: u.ID, Name: u.Name, Symbol: u.Symbol}
+}
+
+func (h *Handler) List(c *gin.Context) {
+	list, err := h.service.List(c.Request.Context())
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to list units"})
+		return
+	}
+	resp := make([]unitResponse, 0, len(list))
+	for _, u := range list {
+		resp = append(resp, toResponse(u))
+	}
+	c.JSON(http.StatusOK, gin.H{"units": resp})
+}
+
+type upsertRequest struct {
+	Name   string `json:"name" binding:"required"`
+	Symbol string `json:"symbol" binding:"required"`
+}
+
+func (h *Handler) Create(c *gin.Context) {
+	var req upsertRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	u, err := h.service.Create(c.Request.Context(), req.Name, req.Symbol)
+	if err != nil {
+		if errors.Is(err, ErrSymbolTaken) {
+			c.JSON(http.StatusConflict, gin.H{"error": "symbol already in use"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to create unit"})
+		return
+	}
+	c.JSON(http.StatusCreated, toResponse(u))
+}
+
+func (h *Handler) Update(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	var req upsertRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+	u, err := h.service.Update(c.Request.Context(), id, req.Name, req.Symbol)
+	if err != nil {
+		switch {
+		case errors.Is(err, ErrNotFound):
+			c.JSON(http.StatusNotFound, gin.H{"error": "unit not found"})
+		case errors.Is(err, ErrSymbolTaken):
+			c.JSON(http.StatusConflict, gin.H{"error": "symbol already in use"})
+		default:
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to update unit"})
+		}
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(u))
+}
+
+func (h *Handler) Delete(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	if err := h.service.Delete(c.Request.Context(), id); err != nil {
+		switch {
+		case errors.Is(err, ErrNotFound):
+			c.JSON(http.StatusNotFound, gin.H{"error": "unit not found"})
+		case errors.Is(err, ErrInUse):
+			c.JSON(http.StatusConflict, gin.H{"error": "unit is used by existing price tiers"})
+		default:
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to delete unit"})
+		}
+		return
+	}
+	c.Status(http.StatusNoContent)
+}

backend/internal/modules/units/model.go

@@ -0,0 +1,19 @@
+// Package units lets the admin define their own measurement units
+// (kg, g, piece, carton, ...) instead of the code hard-coding a fixed list.
+package units
+
+import (
+	"time"
+
+	"github.com/google/uuid"
+)
+
+type Unit struct {
+	ID        uuid.UUID `gorm:"type:uuid;primaryKey"`
+	Name      string    `gorm:"not null"`
+	Symbol    string    `gorm:"uniqueIndex;not null"`
+	CreatedAt time.Time
+	UpdatedAt time.Time
+}
+
+func (Unit) TableName() string { return "units" }

backend/internal/modules/units/repository.go

@@ -0,0 +1,94 @@
+package units
+
+import (
+	"context"
+	"errors"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgconn"
+	"gorm.io/gorm"
+)
+
+var (
+	ErrNotFound    = errors.New("unit not found")
+	ErrSymbolTaken = errors.New("symbol already in use")
+	ErrInUse       = errors.New("unit is referenced by existing price tiers")
+)
+
+type Repository interface {
+	Create(ctx context.Context, u *Unit) error
+	FindByID(ctx context.Context, id uuid.UUID) (*Unit, error)
+	List(ctx context.Context) ([]*Unit, error)
+	Update(ctx context.Context, u *Unit) error
+	Delete(ctx context.Context, id uuid.UUID) error
+}
+
+type gormRepository struct {
+	db *gorm.DB
+}
+
+func NewRepository(db *gorm.DB) Repository {
+	return &gormRepository{db: db}
+}
+
+func (r *gormRepository) Create(ctx context.Context, u *Unit) error {
+	if err := r.db.WithContext(ctx).Create(u).Error; err != nil {
+		if isUniqueViolation(err) {
+			return ErrSymbolTaken
+		}
+		return err
+	}
+	return nil
+}
+
+func (r *gormRepository) FindByID(ctx context.Context, id uuid.UUID) (*Unit, error) {
+	var u Unit
+	err := r.db.WithContext(ctx).Where("id = ?", id).First(&u).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &u, nil
+}
+
+func (r *gormRepository) List(ctx context.Context) ([]*Unit, error) {
+	var list []*Unit
+	if err := r.db.WithContext(ctx).Order("name asc").Find(&list).Error; err != nil {
+		return nil, err
+	}
+	return list, nil
+}
+
+func (r *gormRepository) Update(ctx context.Context, u *Unit) error {
+	err := r.db.WithContext(ctx).Save(u).Error
+	if isUniqueViolation(err) {
+		return ErrSymbolTaken
+	}
+	return err
+}
+
+func (r *gormRepository) Delete(ctx context.Context, id uuid.UUID) error {
+	res := r.db.WithContext(ctx).Delete(&Unit{}, "id = ?", id)
+	if res.Error != nil {
+		if isForeignKeyViolation(res.Error) {
+			return ErrInUse
+		}
+		return res.Error
+	}
+	if res.RowsAffected == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
+func isUniqueViolation(err error) bool {
+	var pgErr *pgconn.PgError
+	return errors.As(err, &pgErr) && pgErr.Code == "23505"
+}
+
+func isForeignKeyViolation(err error) bool {
+	var pgErr *pgconn.PgError
+	return errors.As(err, &pgErr) && pgErr.Code == "23503"
+}

backend/internal/modules/units/routes.go

@@ -0,0 +1,11 @@
+package units
+
+import "github.com/gin-gonic/gin"
+
+func RegisterAdminRoutes(rg *gin.RouterGroup, h *Handler, requireAdmin gin.HandlerFunc) {
+	group := rg.Group("/admin/units", requireAdmin)
+	group.GET("", h.List)
+	group.POST("", h.Create)
+	group.PUT("/:id", h.Update)
+	group.DELETE("/:id", h.Delete)
+}

backend/internal/modules/units/service.go

@@ -0,0 +1,48 @@
+package units
+
+import (
+	"context"
+
+	"github.com/google/uuid"
+)
+
+type Service struct {
+	repo Repository
+}
+
+func NewService(repo Repository) *Service {
+	return &Service{repo: repo}
+}
+
+func (s *Service) List(ctx context.Context) ([]*Unit, error) {
+	return s.repo.List(ctx)
+}
+
+func (s *Service) Get(ctx context.Context, id uuid.UUID) (*Unit, error) {
+	return s.repo.FindByID(ctx, id)
+}
+
+func (s *Service) Create(ctx context.Context, name, symbol string) (*Unit, error) {
+	u := &Unit{ID: uuid.New(), Name: name, Symbol: symbol}
+	if err := s.repo.Create(ctx, u); err != nil {
+		return nil, err
+	}
+	return u, nil
+}
+
+func (s *Service) Update(ctx context.Context, id uuid.UUID, name, symbol string) (*Unit, error) {
+	u, err := s.repo.FindByID(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	u.Name = name
+	u.Symbol = symbol
+	if err := s.repo.Update(ctx, u); err != nil {
+		return nil, err
+	}
+	return u, nil
+}
+
+func (s *Service) Delete(ctx context.Context, id uuid.UUID) error {
+	return s.repo.Delete(ctx, id)
+}

backend/internal/modules/users/handler.go

@@ -0,0 +1,134 @@
+package users
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+)
+
+type Handler struct {
+	service *Service
+}
+
+func NewHandler(service *Service) *Handler {
+	return &Handler{service: service}
+}
+
+type userResponse struct {
+	ID       uuid.UUID `json:"id"`
+	Email    string    `json:"email"`
+	Role     string    `json:"role"`
+	IsActive bool      `json:"is_active"`
+}
+
+func toResponse(u *User) userResponse {
+	return userResponse{ID: u.ID, Email: u.Email, Role: u.Role, IsActive: u.IsActive}
+}
+
+func (h *Handler) List(c *gin.Context) {
+	list, err := h.service.List(c.Request.Context())
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to list users"})
+		return
+	}
+	resp := make([]userResponse, 0, len(list))
+	for _, u := range list {
+		resp = append(resp, toResponse(u))
+	}
+	c.JSON(http.StatusOK, gin.H{"users": resp})
+}
+
+type createUserRequest struct {
+	Email    string `json:"email" binding:"required,email"`
+	Password string `json:"password" binding:"required,min=12"`
+	Role     string `json:"role" binding:"required,oneof=admin customer"`
+}
+
+func (h *Handler) Create(c *gin.Context) {
+	var req createUserRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+
+	user, err := h.service.Create(c.Request.Context(), req.Email, req.Password, req.Role)
+	if err != nil {
+		if errors.Is(err, ErrEmailTaken) {
+			c.JSON(http.StatusConflict, gin.H{"error": "email already in use"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to create user"})
+		return
+	}
+	c.JSON(http.StatusCreated, toResponse(user))
+}
+
+func (h *Handler) Get(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	user, err := h.service.FindByID(c.Request.Context(), id)
+	if err != nil {
+		if errors.Is(err, ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "user not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to get user"})
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(user))
+}
+
+type updateUserRequest struct {
+	Email    string `json:"email" binding:"required,email"`
+	IsActive bool   `json:"is_active"`
+}
+
+func (h *Handler) Update(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	var req updateUserRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "validation error", "details": err.Error()})
+		return
+	}
+
+	user, err := h.service.UpdateProfile(c.Request.Context(), id, req.Email, req.IsActive)
+	if err != nil {
+		if errors.Is(err, ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "user not found"})
+			return
+		}
+		if errors.Is(err, ErrEmailTaken) {
+			c.JSON(http.StatusConflict, gin.H{"error": "email already in use"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to update user"})
+		return
+	}
+	c.JSON(http.StatusOK, toResponse(user))
+}
+
+func (h *Handler) Delete(c *gin.Context) {
+	id, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
+		return
+	}
+	if err := h.service.Delete(c.Request.Context(), id); err != nil {
+		if errors.Is(err, ErrNotFound) {
+			c.JSON(http.StatusNotFound, gin.H{"error": "user not found"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to delete user"})
+		return
+	}
+	c.Status(http.StatusNoContent)
+}

backend/internal/modules/users/model.go

@@ -0,0 +1,27 @@
+// Package users owns the user account entity and its CRUD operations.
+// The auth module depends on this package to look up credentials, but
+// never owns or duplicates the User model itself.
+package users
+
+import (
+	"time"
+
+	"github.com/google/uuid"
+)
+
+const (
+	RoleAdmin    = "admin"
+	RoleCustomer = "customer"
+)
+
+type User struct {
+	ID           uuid.UUID `gorm:"type:uuid;primaryKey"`
+	Email        string    `gorm:"uniqueIndex;not null"`
+	PasswordHash string    `gorm:"not null"`
+	Role         string    `gorm:"not null;default:admin"`
+	IsActive     bool      `gorm:"not null;default:true"`
+	CreatedAt    time.Time
+	UpdatedAt    time.Time
+}
+
+func (User) TableName() string { return "users" }

backend/internal/modules/users/repository.go

@@ -0,0 +1,98 @@
+package users
+
+import (
+	"context"
+	"errors"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgconn"
+	"gorm.io/gorm"
+)
+
+var ErrNotFound = errors.New("user not found")
+var ErrEmailTaken = errors.New("email already in use")
+
+type Repository interface {
+	Create(ctx context.Context, user *User) error
+	FindByEmail(ctx context.Context, email string) (*User, error)
+	FindByID(ctx context.Context, id uuid.UUID) (*User, error)
+	List(ctx context.Context) ([]*User, error)
+	Update(ctx context.Context, user *User) error
+	Delete(ctx context.Context, id uuid.UUID) error
+}
+
+type gormRepository struct {
+	db *gorm.DB
+}
+
+func NewRepository(db *gorm.DB) Repository {
+	return &gormRepository{db: db}
+}
+
+func (r *gormRepository) Create(ctx context.Context, user *User) error {
+	if err := r.db.WithContext(ctx).Create(user).Error; err != nil {
+		if isUniqueViolation(err) {
+			return ErrEmailTaken
+		}
+		return err
+	}
+	return nil
+}
+
+func (r *gormRepository) FindByEmail(ctx context.Context, email string) (*User, error) {
+	var user User
+	err := r.db.WithContext(ctx).Where("email = ?", email).First(&user).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &user, nil
+}
+
+func (r *gormRepository) FindByID(ctx context.Context, id uuid.UUID) (*User, error) {
+	var user User
+	err := r.db.WithContext(ctx).Where("id = ?", id).First(&user).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &user, nil
+}
+
+func (r *gormRepository) List(ctx context.Context) ([]*User, error) {
+	var list []*User
+	if err := r.db.WithContext(ctx).Order("created_at asc").Find(&list).Error; err != nil {
+		return nil, err
+	}
+	return list, nil
+}
+
+func (r *gormRepository) Update(ctx context.Context, user *User) error {
+	err := r.db.WithContext(ctx).Save(user).Error
+	if isUniqueViolation(err) {
+		return ErrEmailTaken
+	}
+	return err
+}
+
+func (r *gormRepository) Delete(ctx context.Context, id uuid.UUID) error {
+	res := r.db.WithContext(ctx).Delete(&User{}, "id = ?", id)
+	if res.Error != nil {
+		return res.Error
+	}
+	if res.RowsAffected == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
+// isUniqueViolation reports whether err is a Postgres unique-constraint
+// violation (SQLSTATE 23505), e.g. a duplicate email.
+func isUniqueViolation(err error) bool {
+	var pgErr *pgconn.PgError
+	return errors.As(err, &pgErr) && pgErr.Code == "23505"
+}

backend/internal/modules/users/routes.go

@@ -0,0 +1,14 @@
+package users
+
+import "github.com/gin-gonic/gin"
+
+// RegisterAdminRoutes mounts the user-management endpoints under the given
+// group, guarded by the requireAdmin middleware supplied by the caller.
+func RegisterAdminRoutes(rg *gin.RouterGroup, h *Handler, requireAdmin gin.HandlerFunc) {
+	group := rg.Group("/admin/users", requireAdmin)
+	group.GET("", h.List)
+	group.POST("", h.Create)
+	group.GET("/:id", h.Get)
+	group.PUT("/:id", h.Update)
+	group.DELETE("/:id", h.Delete)
+}

backend/internal/modules/users/service.go

@@ -0,0 +1,83 @@
+package users
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/google/uuid"
+
+	"backend/internal/platform/security"
+)
+
+type Service struct {
+	repo Repository
+}
+
+func NewService(repo Repository) *Service {
+	return &Service{repo: repo}
+}
+
+func (s *Service) List(ctx context.Context) ([]*User, error) {
+	return s.repo.List(ctx)
+}
+
+func (s *Service) FindByID(ctx context.Context, id uuid.UUID) (*User, error) {
+	return s.repo.FindByID(ctx, id)
+}
+
+func (s *Service) FindByEmail(ctx context.Context, email string) (*User, error) {
+	return s.repo.FindByEmail(ctx, email)
+}
+
+func (s *Service) Create(ctx context.Context, email, password, role string) (*User, error) {
+	if role != RoleAdmin && role != RoleCustomer {
+		return nil, fmt.Errorf("invalid role %q", role)
+	}
+	hash, err := security.HashPassword(password)
+	if err != nil {
+		return nil, fmt.Errorf("hash password: %w", err)
+	}
+
+	user := &User{
+		ID:           uuid.New(),
+		Email:        email,
+		PasswordHash: hash,
+		Role:         role,
+		IsActive:     true,
+	}
+	if err := s.repo.Create(ctx, user); err != nil {
+		return nil, err
+	}
+	return user, nil
+}
+
+// UpdateProfile updates the mutable, non-security fields of a user.
+func (s *Service) UpdateProfile(ctx context.Context, id uuid.UUID, email string, isActive bool) (*User, error) {
+	user, err := s.repo.FindByID(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	user.Email = email
+	user.IsActive = isActive
+	if err := s.repo.Update(ctx, user); err != nil {
+		return nil, err
+	}
+	return user, nil
+}
+
+func (s *Service) SetPassword(ctx context.Context, id uuid.UUID, newPassword string) error {
+	user, err := s.repo.FindByID(ctx, id)
+	if err != nil {
+		return err
+	}
+	hash, err := security.HashPassword(newPassword)
+	if err != nil {
+		return fmt.Errorf("hash password: %w", err)
+	}
+	user.PasswordHash = hash
+	return s.repo.Update(ctx, user)
+}
+
+func (s *Service) Delete(ctx context.Context, id uuid.UUID) error {
+	return s.repo.Delete(ctx, id)
+}