fix: Add mounted checks and fix memory leaks across UI components

Address potential memory leaks and state-after-dispose issues:

- AppProvider: Add dispose method to clean up listeners and callbacks
- MapTab: Store and restore original location callback instead of nullifying
- MessagesTab: Use Timer instead of Future.delayed for highlight cleanup
- ConnectionDialog: Use named listener method for proper tab controller cleanup
- RoomLoginSheet: Add _isDisposed flag to handle async callback race conditions
- SettingsScreen: Clear location service callbacks in dispose
- Various screens: Add mounted checks before setState after async operations
  (contacts_tab, device_config, home_screen, map_management, packet_log,
   sar_template_management, sar_update_sheet, permission_request_dialog)

lib/screens/contacts_tab.dart

@@ -51,9 +51,11 @@ class _ContactsTabState extends State<ContactsTab> {
   }
 
   Future<void> _handleRefresh() async {
+    if (!mounted) return;
     final appProvider = context.read<AppProvider>();
     await appProvider.refresh();
     // Also refresh location
+    if (!mounted) return;
     await _getCurrentLocation();
   }