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>

client/pubspec.yaml

@@ -0,0 +1,48 @@
+name: food_ai
+description: "FoodAI - AI-powered food management"
+publish_to: 'none'
+version: 1.0.0+1
+
+environment:
+  sdk: ^3.9.2
+
+dependencies:
+  flutter:
+    sdk: flutter
+
+  cupertino_icons: ^1.0.8
+
+  # Navigation
+  go_router: ^14.0.0
+
+  # State management
+  flutter_riverpod: ^2.5.0
+
+  # Network
+  dio: ^5.4.0
+
+  # Firebase
+  firebase_core: ^3.0.0
+  firebase_auth: ^5.0.0
+  google_sign_in: ^6.2.0
+
+  # Storage
+  flutter_secure_storage: ^9.2.0
+
+  # Serialization
+  json_annotation: ^4.9.0
+
+  # UI
+  cached_network_image: ^3.3.0
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+
+  flutter_lints: ^5.0.0
+  json_serializable: ^6.8.0
+  build_runner: ^2.4.0
+  mockito: ^5.4.0
+
+flutter:
+  uses-material-design: true