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/contacts/direct_message_sheet.dart

@@ -41,6 +41,7 @@ class _DirectMessageSheetState extends State<DirectMessageSheet> {
   }
 
   void _updateCharacterCount() {
+    if (!mounted) return;
     setState(() {
       _characterCount = _textController.text.length;
     });

lib/widgets/contacts/room_login_sheet.dart

@@ -21,6 +21,7 @@ class _RoomLoginSheetState extends State<RoomLoginSheet> {
   final FocusNode _focusNode = FocusNode();
   bool _isLoggingIn = false;
   bool _obscurePassword = true;
+  bool _isDisposed = false; // Track disposal state for async callbacks
 
   @override
   void initState() {
@@ -30,6 +31,7 @@ class _RoomLoginSheetState extends State<RoomLoginSheet> {
 
   @override
   void dispose() {
+    _isDisposed = true;
     _passwordController.dispose();
     _focusNode.dispose();
     super.dispose();
@@ -245,15 +247,15 @@ class _RoomLoginSheetState extends State<RoomLoginSheet> {
         '   Messages will be fetched when onMessageWaiting callback is triggered',
       );
 
-      if (mounted) {
-        ScaffoldMessenger.of(context).showSnackBar(
-          SnackBar(
-            content: Text(AppLocalizations.of(context)!.loggedInSuccessfully),
-            backgroundColor: Theme.of(context).colorScheme.primary,
-            duration: const Duration(seconds: 3),
-          ),
-        );
-      }
+      // Check both _isDisposed flag and mounted to handle race conditions
+      if (_isDisposed || !mounted) return;
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(
+          content: Text(AppLocalizations.of(context)!.loggedInSuccessfully),
+          backgroundColor: Theme.of(context).colorScheme.primary,
+          duration: const Duration(seconds: 3),
+        ),
+      );
     };
 
     connectionProvider.onLoginFail = (publicKeyPrefix) {
@@ -263,15 +265,15 @@ class _RoomLoginSheetState extends State<RoomLoginSheet> {
 
       debugPrint('❌ [RoomLogin] Login failed - incorrect password');
 
-      if (mounted) {
-        ScaffoldMessenger.of(context).showSnackBar(
-          SnackBar(
-            content: Text(AppLocalizations.of(context)!.loginFailed),
-            backgroundColor: Theme.of(context).colorScheme.error,
-            duration: const Duration(seconds: 3),
-          ),
-        );
-      }
+      // Check both _isDisposed flag and mounted to handle race conditions
+      if (_isDisposed || !mounted) return;
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(
+          content: Text(AppLocalizations.of(context)!.loginFailed),
+          backgroundColor: Theme.of(context).colorScheme.error,
+          duration: const Duration(seconds: 3),
+        ),
+      );
     };
 
     try {