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/core/theme/app_colors.dart

@@ -0,0 +1,29 @@
+import 'package:flutter/material.dart';
+
+abstract class AppColors {
+  // Primary
+  static const primary = Color(0xFF4CAF50);
+  static const primaryLight = Color(0xFF81C784);
+  static const primaryDark = Color(0xFF388E3C);
+
+  // Accent
+  static const accent = Color(0xFFFF9800);
+
+  // Background
+  static const background = Color(0xFFF5F5F5);
+  static const surface = Color(0xFFFFFFFF);
+
+  // Text
+  static const textPrimary = Color(0xFF212121);
+  static const textSecondary = Color(0xFF757575);
+
+  // Status
+  static const error = Color(0xFFE53935);
+  static const warning = Color(0xFFFFA726);
+  static const success = Color(0xFF66BB6A);
+
+  // Shelf life indicators
+  static const freshGreen = Color(0xFF4CAF50);
+  static const warningYellow = Color(0xFFFFC107);
+  static const expiredRed = Color(0xFFE53935);
+}

client/lib/core/theme/app_theme.dart

@@ -0,0 +1,31 @@
+import 'package:flutter/material.dart';
+import 'app_colors.dart';
+
+ThemeData appTheme() {
+  return ThemeData(
+    useMaterial3: true,
+    colorSchemeSeed: AppColors.primary,
+    scaffoldBackgroundColor: AppColors.background,
+    appBarTheme: const AppBarTheme(
+      centerTitle: true,
+      elevation: 0,
+      backgroundColor: AppColors.surface,
+      foregroundColor: AppColors.textPrimary,
+    ),
+    bottomNavigationBarTheme: const BottomNavigationBarThemeData(
+      selectedItemColor: AppColors.primary,
+      unselectedItemColor: AppColors.textSecondary,
+      type: BottomNavigationBarType.fixed,
+    ),
+    inputDecorationTheme: InputDecorationTheme(
+      border: OutlineInputBorder(borderRadius: BorderRadius.circular(12)),
+      contentPadding: const EdgeInsets.symmetric(horizontal: 16, vertical: 12),
+    ),
+    elevatedButtonTheme: ElevatedButtonThemeData(
+      style: ElevatedButton.styleFrom(
+        minimumSize: const Size(double.infinity, 48),
+        shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(12)),
+      ),
+    ),
+  );
+}