refactor: cleanup dead code from reminder system
- Remove permission fallback logic from LocalNotificationService
- Remove unused methods: _scheduleInApp*, _trackFallback, bindInAppReminderHandler
- Remove unused fields: _permissionFallbackTracker, _inAppReminderHandler, _inAppFallbackTimersByEventId, _canDeliverSystemNotification
- Remove unused _showSnoozeOptions from ReminderOverlay
- Remove unused reminderActionExecutor from AuthSessionBootstrapper
- Remove obsolete test files: reminder_permission_fallback_test, reminder_notification_bridge_test, auth_session_bootstrapper_test
- Add native notification grouping (threadIdentifier/groupKey)
qzl
d17f5d78aa