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/providers/app_provider.dart

@@ -25,6 +25,8 @@ class AppProvider with ChangeNotifier {
   bool _isInitialized = false;
   bool get isInitialized => _isInitialized;
 
+  bool _isDisposed = false;
+
   bool _isSimpleMode = true;
   bool get isSimpleMode => _isSimpleMode;
 
@@ -683,4 +685,17 @@ class AppProvider with ChangeNotifier {
       'sarMarkers': messagesProvider.sarMarkerStats,
     };
   }
+
+  @override
+  void dispose() {
+    _isDisposed = true;
+    // Remove connection state listener
+    connectionProvider.removeListener(_handleConnectionStateChange);
+    // Clear location service callbacks
+    locationTrackingService.onPositionUpdate = null;
+    locationTrackingService.onBroadcastSent = null;
+    locationTrackingService.onError = null;
+    locationTrackingService.onTrackingStateChanged = null;
+    super.dispose();
+  }
 }