feat: implement Iteration 0 foundation (backend + Flutter client)

Backend (Go):
- Project structure with chi router, pgxpool, goose migrations
- JWT auth (access/refresh tokens) with Firebase token verification
- NoopTokenVerifier for local dev without Firebase credentials
- PostgreSQL user repository with atomic profile updates (transactions)
- Mifflin-St Jeor calorie calculation based on profile data
- REST API: POST /auth/login, /auth/refresh, /auth/logout, GET/PUT /profile, GET /health
- Middleware: auth, CORS (localhost wildcard), logging, recovery, request_id
- Unit tests (51 passing) and integration tests (testcontainers)
- Docker Compose setup with postgres healthcheck and graceful shutdown

Flutter client:
- Riverpod state management with GoRouter navigation
- Firebase Auth (email/password + Google sign-in with web popup support)
- Platform-aware API URLs (web/Android/iOS)
- Dio HTTP client with JWT auth interceptor and concurrent refresh handling
- Secure token storage
- Screens: Login, Register, Home (tabs: Menu, Recipes, Products, Profile)
- Unit tests (17 passing)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/user/mocks/repository.go

@@ -0,0 +1,46 @@
+package mocks
+
+import (
+	"context"
+	"time"
+
+	"github.com/food-ai/backend/internal/user"
+)
+
+type MockUserRepository struct {
+	UpsertByFirebaseUIDFn func(ctx context.Context, uid, email, name, avatarURL string) (*user.User, error)
+	GetByIDFn             func(ctx context.Context, id string) (*user.User, error)
+	UpdateFn              func(ctx context.Context, id string, req user.UpdateProfileRequest) (*user.User, error)
+	UpdateInTxFn          func(ctx context.Context, id string, profileReq user.UpdateProfileRequest, caloriesReq *user.UpdateProfileRequest) (*user.User, error)
+	SetRefreshTokenFn     func(ctx context.Context, id, token string, expiresAt time.Time) error
+	FindByRefreshTokenFn  func(ctx context.Context, token string) (*user.User, error)
+	ClearRefreshTokenFn   func(ctx context.Context, id string) error
+}
+
+func (m *MockUserRepository) UpsertByFirebaseUID(ctx context.Context, uid, email, name, avatarURL string) (*user.User, error) {
+	return m.UpsertByFirebaseUIDFn(ctx, uid, email, name, avatarURL)
+}
+
+func (m *MockUserRepository) GetByID(ctx context.Context, id string) (*user.User, error) {
+	return m.GetByIDFn(ctx, id)
+}
+
+func (m *MockUserRepository) Update(ctx context.Context, id string, req user.UpdateProfileRequest) (*user.User, error) {
+	return m.UpdateFn(ctx, id, req)
+}
+
+func (m *MockUserRepository) UpdateInTx(ctx context.Context, id string, profileReq user.UpdateProfileRequest, caloriesReq *user.UpdateProfileRequest) (*user.User, error) {
+	return m.UpdateInTxFn(ctx, id, profileReq, caloriesReq)
+}
+
+func (m *MockUserRepository) SetRefreshToken(ctx context.Context, id, token string, expiresAt time.Time) error {
+	return m.SetRefreshTokenFn(ctx, id, token, expiresAt)
+}
+
+func (m *MockUserRepository) FindByRefreshToken(ctx context.Context, token string) (*user.User, error) {
+	return m.FindByRefreshTokenFn(ctx, token)
+}
+
+func (m *MockUserRepository) ClearRefreshToken(ctx context.Context, id string) error {
+	return m.ClearRefreshTokenFn(ctx, id)
+}