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/web/manifest.json

@@ -0,0 +1,35 @@
+{
+    "name": "food_ai",
+    "short_name": "food_ai",
+    "start_url": ".",
+    "display": "standalone",
+    "background_color": "#0175C2",
+    "theme_color": "#0175C2",
+    "description": "A new Flutter project.",
+    "orientation": "portrait-primary",
+    "prefer_related_applications": false,
+    "icons": [
+        {
+            "src": "icons/Icon-192.png",
+            "sizes": "192x192",
+            "type": "image/png"
+        },
+        {
+            "src": "icons/Icon-512.png",
+            "sizes": "512x512",
+            "type": "image/png"
+        },
+        {
+            "src": "icons/Icon-maskable-192.png",
+            "sizes": "192x192",
+            "type": "image/png",
+            "purpose": "maskable"
+        },
+        {
+            "src": "icons/Icon-maskable-512.png",
+            "sizes": "512x512",
+            "type": "image/png",
+            "purpose": "maskable"
+        }
+    ]
+}