feat(eq): android auto custom equalizer and robust device detection

- MainActivity: onListen re-emits the current active device and registers
  the audio device callback idempotently, so recreated activities resync
  instead of freezing the active-device id on a disconnected device.
- servicio_dispositivo_audio: resubscribir() re-opens the event channel;
  estado_ecualizador exposes refrescarDispositivoActual() with an
  in-flight guard, invoked on app resume and when opening advanced EQ
  options, clearing stale green-dot device selections.
- navegacion_auto/servicio_audio: new 'Personalizado' browse tree in
  Android Auto (5 band folders, 13 gain steps each) applied live via
  setBanda; preset and gain taps persist at device level when
  multi-device EQ is active and respect station/matrix overrides,
  with apply-before-persist ordering and children-changed notifications.
- l10n: regenerate stale generated localizations; add rxdart as direct
  dependency for the subscribeToChildren override.

lib/pantallas/pantalla_ajustes.dart

@@ -779,9 +779,26 @@ class _SeccionEcualizador extends StatelessWidget {
 /// Always shows the feature toggle so the user can discover it. When the
 /// toggle is OFF, the device list is completely absent (not just invisible),
 /// matching the spec scenario "Settings section is absent when toggle is off".
-class _SeccionEcualizadorAvanzado extends StatelessWidget {
+class _SeccionEcualizadorAvanzado extends StatefulWidget {
   const _SeccionEcualizadorAvanzado();
 
+  @override
+  State<_SeccionEcualizadorAvanzado> createState() =>
+      _SeccionEcualizadorAvanzadoState();
+}
+
+class _SeccionEcualizadorAvanzadoState
+    extends State<_SeccionEcualizadorAvanzado> {
+  @override
+  void initState() {
+    super.initState();
+    // Fix "stale green dot": refresh the active-device indicator with a
+    // fresh native query the moment this section becomes visible, instead of
+    // trusting the last event that happened to arrive (no-op when the
+    // multi-device toggle is off).
+    unawaited(context.read<EstadoEcualizador>().refrescarDispositivoActual());
+  }
+
   @override
   Widget build(BuildContext context) {
     final l10n = AppLocalizations.of(context);