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/messages/sar_update_sheet.dart

@@ -231,6 +231,7 @@ class _SarUpdateSheetState extends State<SarUpdateSheet> {
     try {
       // Check if location services are enabled
       bool serviceEnabled = await Geolocator.isLocationServiceEnabled();
+      if (!mounted) return;
       if (!serviceEnabled) {
         setState(() {
           _locationError = 'Location services are disabled';
@@ -241,8 +242,10 @@ class _SarUpdateSheetState extends State<SarUpdateSheet> {
 
       // Check permissions
       LocationPermission permission = await Geolocator.checkPermission();
+      if (!mounted) return;
       if (permission == LocationPermission.denied) {
         permission = await Geolocator.requestPermission();
+        if (!mounted) return;
         if (permission == LocationPermission.denied) {
           setState(() {
             _locationError = 'Location permission denied';