fix: address PR review issues

- Fix memory leak by adding dispose() to remove connection listener
- Fix typo: changedNavgation -> _changedNavigation
- Add mounted check before navigation to prevent errors
- Remove overly aggressive _handleDisconnection() call on battery request failure
- Only reset battery flag on error to allow retry without disconnecting

lib/connector/meshcore_connector.dart

@@ -963,7 +963,7 @@ class MeshCoreConnector extends ChangeNotifier {
       await sendFrame(buildGetBattAndStorageFrame());
     } catch (e) {
       // Reset flag on error to allow retry
-      _handleDisconnection();
+      // Don't disconnect on battery request failure - it may be transient
       _batteryRequested = false;
     }
   }