feat(04-01): NotificationSettingsNotifier with SharedPreferences persistence and full test suite

- Fix NotificationService API calls to use flutter_local_notifications v21 named parameters
- Expose nextInstanceOf as @visibleForTesting public method for unit testing
- Create NotificationSettingsNotifier with @Riverpod(keepAlive: true)
- NotificationSettings data class with enabled bool + TimeOfDay fields
- Persist notifications_enabled, notifications_hour, notifications_minute to SharedPreferences
- Sync default state in build(), async _load() overrides on hydration
- Update tests to use correct Riverpod 3 provider name (notificationSettingsProvider)
- Add makeContainer() helper to await initial _load() before asserting mutations
- All 84 tests pass (72 existing + 12 new notification tests)

lib/core/notifications/notification_service.dart

@@ -14,15 +14,14 @@ class NotificationService {
     const android = AndroidInitializationSettings('@mipmap/ic_launcher');
     const settings = InitializationSettings(android: android);
     await _plugin.initialize(
-      settings,
+      settings: settings,
       onDidReceiveNotificationResponse: _onTap,
     );
   }
 
   Future<bool> requestPermission() async {
-    final android = _plugin
-        .resolvePlatformSpecificImplementation<
-            AndroidFlutterLocalNotificationsPlugin>();
+    final android = _plugin.resolvePlatformSpecificImplementation<
+        AndroidFlutterLocalNotificationsPlugin>();
     return await android?.requestNotificationsPermission() ?? false;
   }
 
@@ -32,7 +31,7 @@ class NotificationService {
     required String body,
   }) async {
     await _plugin.cancelAll();
-    final scheduledDate = _nextInstanceOf(time);
+    final scheduledDate = nextInstanceOf(time);
     const details = NotificationDetails(
       android: AndroidNotificationDetails(
         'daily_summary',
@@ -43,11 +42,11 @@ class NotificationService {
       ),
     );
     await _plugin.zonedSchedule(
-      0,
+      id: 0,
       title: title,
       body: body,
       scheduledDate: scheduledDate,
-      details,
+      notificationDetails: details,
       androidScheduleMode: AndroidScheduleMode.inexactAllowWhileIdle,
       matchDateTimeComponents: DateTimeComponents.time,
     );