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/app.dart

@@ -96,7 +96,8 @@ class _PaginaPrincipal extends StatefulWidget {
   State<_PaginaPrincipal> createState() => _PaginaPrincipalState();
 }
 
-class _PaginaPrincipalState extends State<_PaginaPrincipal> {
+class _PaginaPrincipalState extends State<_PaginaPrincipal>
+    with WidgetsBindingObserver {
   int _indice = 0;
   StreamSubscription<String>? _errorSubscription;
   StreamSubscription<EventoAlarmaAndroid>? _alarmaSubscription;
@@ -124,6 +125,22 @@ class _PaginaPrincipalState extends State<_PaginaPrincipal> {
     PluriNavItem(glyph: PluriIconGlyph.settings, label: l10n.navSettings),
   ];
 
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addObserver(this);
+  }
+
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    if (state != AppLifecycleState.resumed) return;
+    // Fix "stale green dot": on return to foreground the Activity may have
+    // been recreated over the cached engine, leaving the device event channel
+    // without a live native sink. Re-subscribe and re-seed the active device
+    // (no-op when multi-device EQ is off).
+    unawaited(context.read<EstadoEcualizador>().refrescarDispositivoActual());
+  }
+
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
@@ -179,6 +196,7 @@ class _PaginaPrincipalState extends State<_PaginaPrincipal> {
 
   @override
   void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
     _errorSubscription?.cancel();
     _alarmaSubscription?.cancel();
     _alarmaVencidaSubscription?.cancel();