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/shared/models/user.g.dart

@@ -0,0 +1,39 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'user.dart';
+
+// **************************************************************************
+// JsonSerializableGenerator
+// **************************************************************************
+
+User _$UserFromJson(Map<String, dynamic> json) => User(
+  id: json['id'] as String,
+  email: json['email'] as String,
+  name: json['name'] as String,
+  avatarUrl: json['avatar_url'] as String?,
+  heightCm: (json['height_cm'] as num?)?.toInt(),
+  weightKg: (json['weight_kg'] as num?)?.toDouble(),
+  age: (json['age'] as num?)?.toInt(),
+  gender: json['gender'] as String?,
+  activity: json['activity'] as String?,
+  goal: json['goal'] as String?,
+  dailyCalories: (json['daily_calories'] as num?)?.toInt(),
+  plan: json['plan'] as String,
+  preferences: json['preferences'] as Map<String, dynamic>? ?? {},
+);
+
+Map<String, dynamic> _$UserToJson(User instance) => <String, dynamic>{
+  'id': instance.id,
+  'email': instance.email,
+  'name': instance.name,
+  'avatar_url': instance.avatarUrl,
+  'height_cm': instance.heightCm,
+  'weight_kg': instance.weightKg,
+  'age': instance.age,
+  'gender': instance.gender,
+  'activity': instance.activity,
+  'goal': instance.goal,
+  'daily_calories': instance.dailyCalories,
+  'plan': instance.plan,
+  'preferences': instance.preferences,
+};