Add notification permission flow in settings

lib/features/reminders/scheduling/reminder_scheduler.dart

@@ -7,6 +7,9 @@ abstract class ReminderScheduler {
 
   /// Clears all platform-scheduled reminder jobs.
   Future<void> clearAll();
+
+  /// Requests notification permissions where the platform requires them.
+  Future<bool> requestPermissions();
 }
 
 /// Default scheduler used until platform notifications are integrated.
@@ -18,4 +21,7 @@ class NoopReminderScheduler implements ReminderScheduler {
 
   @override
   Future<void> reconcile(List<ReminderRule> reminders) async {}
+
+  @override
+  Future<bool> requestPermissions() async => true;
 }