fix(auto): clear stuck bluetooth EQ selection on device disconnect

The advanced EQ device list kept the green-dot selection on the last
connected Bluetooth device after it disconnected, instead of falling
back to the default preset.

- MainActivity.kt: onAudioDevicesRemoved recomputed the active output
  device via AudioManager.getDevices(), which can still momentarily
  report the just-removed sink (observed on Bluetooth A2DP). Removed
  device ids are now excluded explicitly instead of trusting
  getDevices() to already be current.
- estado_ecualizador.dart: cambiarMultiDeviceEnabled() re-seeds
  dispositivoActualId from a fresh query when the toggle turns back
  on, matching cargarPersistido(), so a stale id from before the
  toggle flip can't leave the dot pinned to a disconnected device.

lib/estado/estado_ecualizador.dart

@@ -274,6 +274,14 @@ class EstadoEcualizador extends ChangeNotifier {
     _eqMultiDeviceEnabled = habilitado;
     await servicio.guardarToggleMultiDispositivo(habilitado);
     _configurarSuscripcionDispositivo();
+
+    // Re-seed the active device from a fresh query instead of leaving a
+    // stale _dispositivoActualId from before the toggle flip (it would
+    // otherwise only self-correct on the next native device-change event).
+    if (_eqMultiDeviceEnabled) {
+      await _sembrarDispositivoActual();
+    }
+
     if (notificar) notifyListeners();
   }