feat: implement Iteration 5 — home screen dashboard

Backend:
- internal/home: GET /home/summary endpoint
  - Today's meal plan from menu_plans/menu_items
  - Logged calories sum from meal_diary
  - Daily goal from user profile (default 2000)
  - Expiring products within 3 days
  - Last 3 saved recommendations (no AI call on home load)
- Wire homeHandler in server.go and main.go

Flutter:
- shared/models/home_summary.dart: HomeSummary, TodaySummary,
  TodayMealPlan, ExpiringSoon, HomeRecipe
- features/home/home_service.dart + home_provider.dart
- features/home/home_screen.dart: greeting, calorie progress bar,
  today's meals card, expiring banner, quick actions row,
  recommendations horizontal list

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/lib/features/home/home_service.dart

@@ -0,0 +1,19 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../../core/api/api_client.dart';
+import '../../core/auth/auth_provider.dart';
+import '../../shared/models/home_summary.dart';
+
+final homeServiceProvider = Provider<HomeService>((ref) {
+  return HomeService(ref.read(apiClientProvider));
+});
+
+class HomeService {
+  final ApiClient _client;
+  HomeService(this._client);
+
+  Future<HomeSummary> getSummary() async {
+    final json = await _client.get('/home/summary');
+    return HomeSummary.fromJson(json);
+  }
+}