feat(04-02): wire notification settings UI, permission flow, scheduling, and tap navigation

- Convert SettingsScreen from ConsumerWidget to ConsumerStatefulWidget
- Add Benachrichtigungen section between Darstellung and Uber sections
- SwitchListTile with permission request on toggle ON (Android 13+)
- Toggle reverts to OFF on permission denial with SnackBar hint
- AnimatedSize progressive disclosure for time picker row when enabled
- _scheduleNotification() queries DailyPlanDao for task/overdue counts
- Skip notification scheduling when task count is 0
- Notification body includes overdue split when overdue > 0
- _onPickTime() shows Material 3 showTimePicker dialog then reschedules
- Wire router.go('/') in NotificationService._onTap for tap navigation
- Regenerate AppLocalizations with 7 new notification strings from Plan 01 ARB

lib/l10n/app_localizations_de.dart

@@ -210,4 +210,30 @@ class AppLocalizationsDe extends AppLocalizations {
 
   @override
   String get dailyPlanNoTasks => 'Noch keine Aufgaben angelegt';
+
+  @override
+  String get settingsSectionNotifications => 'Benachrichtigungen';
+
+  @override
+  String get notificationsEnabledLabel => 'Tägliche Erinnerung';
+
+  @override
+  String get notificationsTimeLabel => 'Uhrzeit';
+
+  @override
+  String get notificationsPermissionDeniedHint =>
+      'Benachrichtigungen sind in den Systemeinstellungen deaktiviert. Tippe hier, um sie zu aktivieren.';
+
+  @override
+  String get notificationTitle => 'Dein Tagesplan';
+
+  @override
+  String notificationBody(int count) {
+    return '$count Aufgaben fällig';
+  }
+
+  @override
+  String notificationBodyWithOverdue(int count, int overdue) {
+    return '$count Aufgaben fällig ($overdue überfällig)';
+  }
 }