feat: implement Iteration 4 — menu planning, shopping list, diary

Backend:
- Migrations 007 (menu_plans, menu_items, shopping_lists) and
  008 (meal_diary)
- gemini/menu.go: GenerateMenu — 7-day × 3-meal plan via one Groq call
- internal/menu: model, repository (GetByWeek, SaveMenuInTx,
  shopping list CRUD), handler (GET/PUT/DELETE /menu,
  POST /ai/generate-menu, shopping list endpoints)
- internal/diary: model, repository, handler (GET/POST/DELETE /diary)
- Increase server WriteTimeout to 120s for long AI calls
- api_client.go: add patch() and postList() helpers

Flutter:
- shared/models: menu.dart, shopping_item.dart, diary_entry.dart
- features/menu: menu_service.dart, menu_provider.dart
  (MenuNotifier, ShoppingListNotifier, DiaryNotifier with family)
- MenuScreen: 7-day view, week nav, skeleton on generation,
  generate FAB with confirmation dialog
- ShoppingListScreen: items by category, optimistic checkbox toggle
- DiaryScreen: daily entries with swipe-to-delete, add-entry sheet
- Router: /menu/shopping-list and /menu/diary routes

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

client/lib/core/api/api_client.dart

@@ -38,6 +38,17 @@ class ApiClient {
     return response.data;
   }
 
+  Future<void> patch(String path,
+      {dynamic data, Map<String, dynamic>? params}) async {
+    await _dio.patch(path, data: data, queryParameters: params);
+  }
+
+  /// Posts data and expects a JSON array response.
+  Future<List<dynamic>> postList(String path, {dynamic data}) async {
+    final response = await _dio.post(path, data: data);
+    return response.data as List<dynamic>;
+  }
+
   Future<Map<String, dynamic>> delete(String path) async {
     final response = await _dio.delete(path);
     return response.data;