feat: add push notification settings panel integration

- Add PushNotificationSettings interface to settings types
- Update useGenericSettings hook to support push_notifications group
- Create comprehensive PushNotificationSettings component with:
  - General enable/disable toggle
  - Service configuration (worker count, queue size, retry settings)
  - APNs configuration for iOS push notifications
  - FCM configuration for Android push notifications
- Integrate push notifications panel into AdvancedSettingsLayout
- Follow existing settings patterns for consistency
- Include proper validation and form handling

Author: Maphikza