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_settings_notifier.g.dart

@@ -0,0 +1,65 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'notification_settings_notifier.dart';
+
+// **************************************************************************
+// RiverpodGenerator
+// **************************************************************************
+
+// GENERATED CODE - DO NOT MODIFY BY HAND
+// ignore_for_file: type=lint, type=warning
+
+@ProviderFor(NotificationSettingsNotifier)
+final notificationSettingsProvider = NotificationSettingsNotifierProvider._();
+
+final class NotificationSettingsNotifierProvider
+    extends
+        $NotifierProvider<NotificationSettingsNotifier, NotificationSettings> {
+  NotificationSettingsNotifierProvider._()
+    : super(
+        from: null,
+        argument: null,
+        retry: null,
+        name: r'notificationSettingsProvider',
+        isAutoDispose: false,
+        dependencies: null,
+        $allTransitiveDependencies: null,
+      );
+
+  @override
+  String debugGetCreateSourceHash() => _$notificationSettingsNotifierHash();
+
+  @$internal
+  @override
+  NotificationSettingsNotifier create() => NotificationSettingsNotifier();
+
+  /// {@macro riverpod.override_with_value}
+  Override overrideWithValue(NotificationSettings value) {
+    return $ProviderOverride(
+      origin: this,
+      providerOverride: $SyncValueProvider<NotificationSettings>(value),
+    );
+  }
+}
+
+String _$notificationSettingsNotifierHash() =>
+    r'0d04ca73c4724bb84ce8d92608cd238cb362254a';
+
+abstract class _$NotificationSettingsNotifier
+    extends $Notifier<NotificationSettings> {
+  NotificationSettings build();
+  @$mustCallSuper
+  @override
+  void runBuild() {
+    final ref = this.ref as $Ref<NotificationSettings, NotificationSettings>;
+    final element =
+        ref.element
+            as $ClassProviderElement<
+              AnyNotifier<NotificationSettings, NotificationSettings>,
+              NotificationSettings,
+              Object?,
+              Object?
+            >;
+    element.handleCreate(ref, build);
+  }
+}