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/device_config_screen.dart

@@ -347,6 +347,8 @@ class _DeviceConfigScreenState extends State<DeviceConfigScreen> {
         ),
       );
 
+      if (!mounted) return;
+
       setState(() {
         _latController.text = position.latitude.toStringAsFixed(6);
         _lonController.text = position.longitude.toStringAsFixed(6);