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/features/menu/menu_service.dart

@@ -0,0 +1,85 @@
+import '../../core/api/api_client.dart';
+import '../../shared/models/diary_entry.dart';
+import '../../shared/models/menu.dart';
+import '../../shared/models/shopping_item.dart';
+
+class MenuService {
+  final ApiClient _client;
+
+  MenuService(this._client);
+
+  // ── Menu ──────────────────────────────────────────────────
+
+  Future<MenuPlan?> getMenu({String? week}) async {
+    final params = <String, dynamic>{};
+    if (week != null) params['week'] = week;
+    final data = await _client.get('/menu', params: params);
+    // Backend returns {"week_start": "...", "days": null} when no plan exists.
+    if (data['id'] == null) return null;
+    return MenuPlan.fromJson(data);
+  }
+
+  Future<MenuPlan> generateMenu({String? week}) async {
+    final body = <String, dynamic>{};
+    if (week != null) body['week'] = week;
+    final data = await _client.post('/ai/generate-menu', data: body);
+    return MenuPlan.fromJson(data);
+  }
+
+  Future<void> updateMenuItem(String itemId, String recipeId) async {
+    await _client.put('/menu/items/$itemId', data: {'recipe_id': recipeId});
+  }
+
+  Future<void> deleteMenuItem(String itemId) async {
+    await _client.deleteVoid('/menu/items/$itemId');
+  }
+
+  // ── Shopping list ─────────────────────────────────────────
+
+  Future<List<ShoppingItem>> getShoppingList({String? week}) async {
+    final params = <String, dynamic>{};
+    if (week != null) params['week'] = week;
+    final data = await _client.getList('/shopping-list', params: params);
+    return data
+        .map((e) => ShoppingItem.fromJson(e as Map<String, dynamic>))
+        .toList();
+  }
+
+  Future<List<ShoppingItem>> generateShoppingList({String? week}) async {
+    final body = <String, dynamic>{};
+    if (week != null) body['week'] = week;
+    final data = await _client.postList('/shopping-list/generate', data: body);
+    return data
+        .map((e) => ShoppingItem.fromJson(e as Map<String, dynamic>))
+        .toList();
+  }
+
+  Future<void> toggleShoppingItem(int index, bool checked,
+      {String? week}) async {
+    final params = <String, dynamic>{};
+    if (week != null) params['week'] = week;
+    await _client.patch(
+      '/shopping-list/items/$index/check',
+      data: {'checked': checked},
+      params: params,
+    );
+  }
+
+  // ── Diary ─────────────────────────────────────────────────
+
+  Future<List<DiaryEntry>> getDiary(String date) async {
+    final data = await _client.getList('/diary', params: {'date': date});
+    return data
+        .map((e) => DiaryEntry.fromJson(e as Map<String, dynamic>))
+        .toList();
+  }
+
+  Future<DiaryEntry> createDiaryEntry(Map<String, dynamic> body) async {
+    final data = await _client.post('/diary', data: body);
+    return DiaryEntry.fromJson(data);
+  }
+
+  Future<void> deleteDiaryEntry(String id) async {
+    await _client.deleteVoid('/diary/$id');
+  }
+}