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/.metadata

@@ -0,0 +1,36 @@
+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled and should not be manually edited.
+
+version:
+  revision: "a402d9a4376add5bc2d6b1e33e53edaae58c07f8"
+  channel: "stable"
+
+project_type: app
+
+# Tracks metadata for the flutter migrate command
+migration:
+  platforms:
+    - platform: root
+      create_revision: a402d9a4376add5bc2d6b1e33e53edaae58c07f8
+      base_revision: a402d9a4376add5bc2d6b1e33e53edaae58c07f8
+    - platform: android
+      create_revision: a402d9a4376add5bc2d6b1e33e53edaae58c07f8
+      base_revision: a402d9a4376add5bc2d6b1e33e53edaae58c07f8
+    - platform: ios
+      create_revision: a402d9a4376add5bc2d6b1e33e53edaae58c07f8
+      base_revision: a402d9a4376add5bc2d6b1e33e53edaae58c07f8
+    - platform: web
+      create_revision: a402d9a4376add5bc2d6b1e33e53edaae58c07f8
+      base_revision: a402d9a4376add5bc2d6b1e33e53edaae58c07f8
+
+  # User provided section
+
+  # List of Local paths (relative to this file) that should be
+  # ignored by the migrate tool.
+  #
+  # Files that are not part of the templates will be ignored by default.
+  unmanaged_files:
+    - 'lib/main.dart'
+    - 'ios/Runner.xcodeproj/project.pbxproj'