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/lib/firebase_options.dart

@@ -0,0 +1,51 @@
+import 'package:firebase_core/firebase_core.dart' show FirebaseOptions;
+import 'package:flutter/foundation.dart'
+    show defaultTargetPlatform, kIsWeb, TargetPlatform;
+
+class DefaultFirebaseOptions {
+  static FirebaseOptions get currentPlatform {
+    if (kIsWeb) {
+      return web;
+    }
+    switch (defaultTargetPlatform) {
+      case TargetPlatform.android:
+        return android;
+      case TargetPlatform.iOS:
+        return ios;
+      default:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions are not supported for this platform.',
+        );
+    }
+  }
+
+  // Web config — from Firebase Console → Project Settings → Your apps → Web
+  static const FirebaseOptions web = FirebaseOptions(
+    apiKey: 'AIzaSyA9m_zlnQP3T9x0_AZGi5yYH-NQ9C1uPqc',
+    authDomain: 'food-ai-efd52.firebaseapp.com',
+    projectId: 'food-ai-efd52',
+    storageBucket: 'food-ai-efd52.firebasestorage.app',
+    messagingSenderId: '844967109320',
+    appId: '1:844967109320:web:3a1c6307a6d14810fdbbfd',
+    measurementId: 'G-PNKBVM3PDN',
+  );
+
+  // TODO: заполнить после добавления Android-приложения в Firebase Console
+  static const FirebaseOptions android = FirebaseOptions(
+    apiKey: 'YOUR_ANDROID_API_KEY',
+    appId: 'YOUR_ANDROID_APP_ID',
+    messagingSenderId: '844967109320',
+    projectId: 'food-ai-efd52',
+    storageBucket: 'food-ai-efd52.firebasestorage.app',
+  );
+
+  // TODO: заполнить после добавления iOS-приложения в Firebase Console
+  static const FirebaseOptions ios = FirebaseOptions(
+    apiKey: 'YOUR_IOS_API_KEY',
+    appId: 'YOUR_IOS_APP_ID',
+    messagingSenderId: '844967109320',
+    projectId: 'food-ai-efd52',
+    storageBucket: 'food-ai-efd52.firebasestorage.app',
+    iosBundleId: 'com.foodai.foodAi',
+  );
+}