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/settings_screen.dart

@@ -57,6 +57,15 @@ class _SettingsScreenState extends State<SettingsScreen> {
     _loadRxTxPreference();
   }
 
+  @override
+  void dispose() {
+    // Clear location service callbacks to prevent memory leaks
+    _locationService.onError = null;
+    _locationService.onBroadcastSent = null;
+    _locationService.onTrackingStateChanged = null;
+    super.dispose();
+  }
+
   Future<void> _loadPackageInfo() async {
     final info = await PackageInfo.fromPlatform();
     if (mounted) {