fix(flutter): request notification permission proactively (TODO-041)

When user enables poke notifications, call requestPermission()
immediately so OS prompt appears on first enable, not lazily.

apps/chanora_flutter/test/widgets/poke_notification_settings_test.dart

@@ -3,6 +3,7 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
 import 'package:chanora_flutter/l10n/generated/app_localizations.dart';
+import 'package:chanora_flutter/services/poke_notification_service.dart';
 import 'package:chanora_flutter/services/poke_preferences_service.dart';
 import 'package:chanora_flutter/widgets/poke_notification_settings.dart';
 
@@ -14,11 +15,16 @@ void main() {
     await preferences.muteSender(BigInt.from(42));
     addTearDown(preferences.dispose);
 
+    final notificationService = PokeNotificationService();
+
     await tester.pumpWidget(
       MaterialApp(
         localizationsDelegates: AppL10n.localizationsDelegates,
         supportedLocales: AppL10n.supportedLocales,
-        home: PokeNotificationSettingsDialog(preferences: preferences),
+        home: PokeNotificationSettingsDialog(
+          preferences: preferences,
+          notificationService: notificationService,
+        ),
       ),
     );