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_provider.dart

@@ -0,0 +1,147 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../../core/auth/auth_provider.dart';
+import '../../shared/models/diary_entry.dart';
+import '../../shared/models/menu.dart';
+import '../../shared/models/shopping_item.dart';
+import 'menu_service.dart';
+
+// ── Service provider ──────────────────────────────────────────
+
+final menuServiceProvider = Provider<MenuService>((ref) {
+  return MenuService(ref.read(apiClientProvider));
+});
+
+// ── Current week (state) ──────────────────────────────────────
+
+/// The ISO week string for the currently displayed week, e.g. "2026-W08".
+final currentWeekProvider = StateProvider<String>((ref) {
+  final now = DateTime.now().toUtc();
+  final (y, w) = _isoWeek(now);
+  return '$y-W${w.toString().padLeft(2, '0')}';
+});
+
+(int year, int week) _isoWeek(DateTime dt) {
+  // Shift to Thursday to get ISO week year.
+  final thu = dt.add(Duration(days: 4 - (dt.weekday == 7 ? 0 : dt.weekday)));
+  final jan1 = DateTime.utc(thu.year, 1, 1);
+  final week = ((thu.difference(jan1).inDays) / 7).ceil();
+  return (thu.year, week);
+}
+
+// ── Menu notifier ─────────────────────────────────────────────
+
+class MenuNotifier extends StateNotifier<AsyncValue<MenuPlan?>> {
+  final MenuService _service;
+  final String _week;
+
+  MenuNotifier(this._service, this._week) : super(const AsyncValue.loading()) {
+    load();
+  }
+
+  Future<void> load() async {
+    state = const AsyncValue.loading();
+    state = await AsyncValue.guard(() => _service.getMenu(week: _week));
+  }
+
+  Future<void> generate() async {
+    state = const AsyncValue.loading();
+    state = await AsyncValue.guard(() => _service.generateMenu(week: _week));
+  }
+
+  Future<void> updateItem(String itemId, String recipeId) async {
+    await _service.updateMenuItem(itemId, recipeId);
+    await load();
+  }
+
+  Future<void> deleteItem(String itemId) async {
+    await _service.deleteMenuItem(itemId);
+    await load();
+  }
+}
+
+final menuProvider =
+    StateNotifierProvider.family<MenuNotifier, AsyncValue<MenuPlan?>, String>(
+  (ref, week) => MenuNotifier(ref.read(menuServiceProvider), week),
+);
+
+// ── Shopping list notifier ────────────────────────────────────
+
+class ShoppingListNotifier extends StateNotifier<AsyncValue<List<ShoppingItem>>> {
+  final MenuService _service;
+  final String _week;
+
+  ShoppingListNotifier(this._service, this._week)
+      : super(const AsyncValue.loading()) {
+    load();
+  }
+
+  Future<void> load() async {
+    state = const AsyncValue.loading();
+    state = await AsyncValue.guard(() => _service.getShoppingList(week: _week));
+  }
+
+  Future<void> regenerate() async {
+    state = const AsyncValue.loading();
+    state = await AsyncValue.guard(
+        () => _service.generateShoppingList(week: _week));
+  }
+
+  Future<void> toggle(int index, bool checked) async {
+    // Optimistic update.
+    state = state.whenData((items) {
+      final list = List<ShoppingItem>.from(items);
+      if (index < list.length) {
+        list[index] = list[index].copyWith(checked: checked);
+      }
+      return list;
+    });
+    try {
+      await _service.toggleShoppingItem(index, checked, week: _week);
+    } catch (_) {
+      // Revert on failure.
+      await load();
+    }
+  }
+}
+
+final shoppingListProvider = StateNotifierProvider.family<
+    ShoppingListNotifier, AsyncValue<List<ShoppingItem>>, String>(
+  (ref, week) => ShoppingListNotifier(ref.read(menuServiceProvider), week),
+);
+
+// ── Diary notifier ────────────────────────────────────────────
+
+class DiaryNotifier extends StateNotifier<AsyncValue<List<DiaryEntry>>> {
+  final MenuService _service;
+  final String _date;
+
+  DiaryNotifier(this._service, this._date) : super(const AsyncValue.loading()) {
+    load();
+  }
+
+  Future<void> load() async {
+    state = const AsyncValue.loading();
+    state = await AsyncValue.guard(() => _service.getDiary(_date));
+  }
+
+  Future<void> add(Map<String, dynamic> body) async {
+    await _service.createDiaryEntry(body);
+    await load();
+  }
+
+  Future<void> remove(String id) async {
+    final prev = state;
+    state = state.whenData((l) => l.where((e) => e.id != id).toList());
+    try {
+      await _service.deleteDiaryEntry(id);
+    } catch (_) {
+      state = prev;
+    }
+  }
+}
+
+final diaryProvider =
+    StateNotifierProvider.family<DiaryNotifier, AsyncValue<List<DiaryEntry>>, String>(
+  (ref, date) => DiaryNotifier(ref.read(menuServiceProvider), date),
+);