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.

pubspec.yaml

@@ -17,6 +17,9 @@ dependencies:
   just_audio: ^0.9.42
   audio_service: ^0.18.15
   audio_session: ^0.1.21
+  # Ya transitiva vía audio_service; directa para poder emitir
+  # notifyChildrenChanged (subscribeToChildren con BehaviorSubject).
+  rxdart: ^0.28.0
   
   # UI
   cupertino_icons: ^1.0.8