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/widgets/permission_request_dialog.dart

@@ -38,6 +38,7 @@ class _PermissionRequestDialogState extends State<PermissionRequestDialog> {
     try {
       // Check if location service is enabled
       final serviceEnabled = await Geolocator.isLocationServiceEnabled();
+      if (!mounted) return;
       if (!serviceEnabled) {
         setState(() {
           _errorMessage = 'Location services are disabled. Please enable location services in your device settings.';
@@ -48,10 +49,12 @@ class _PermissionRequestDialogState extends State<PermissionRequestDialog> {
 
       // Check current permission
       LocationPermission permission = await Geolocator.checkPermission();
+      if (!mounted) return;
 
       if (permission == LocationPermission.denied) {
         // Request permission
         permission = await Geolocator.requestPermission();
+        if (!mounted) return;
       }
 
       if (permission == LocationPermission.denied) {
@@ -78,11 +81,10 @@ class _PermissionRequestDialogState extends State<PermissionRequestDialog> {
       });
 
       // Close dialog and notify parent
-      if (mounted) {
-        Navigator.of(context).pop();
-        widget.onPermissionsGranted();
-      }
+      Navigator.of(context).pop();
+      widget.onPermissionsGranted();
     } catch (e) {
+      if (!mounted) return;
       setState(() {
         _errorMessage = 'Error requesting permissions: $e';
         _isRequesting = false;