fix(alarms): harden native playback and pre-notice actions

lib/pantallas/pantalla_alarma_sonando.dart

@@ -30,6 +30,7 @@ class _PantallaAlarmaSonandoState extends State<PantallaAlarmaSonando> {
   Timer? _fallbackTimer;
   bool _fallbackActivo = false;
   bool _radioIntentada = false;
+  bool _audioFlutterConfirmado = false;
 
   @override
   void initState() {
@@ -57,6 +58,7 @@ class _PantallaAlarmaSonandoState extends State<PantallaAlarmaSonando> {
     _estadoSub = radio.estadoStream.listen((estado) {
       if (estado == EstadoReproduccion.reproduciendo && mounted) {
         _fallbackTimer?.cancel();
+        _confirmarAudioFlutterListo();
       }
       if (estado == EstadoReproduccion.error && mounted) {
         _iniciarFallback();
@@ -76,9 +78,18 @@ class _PantallaAlarmaSonandoState extends State<PantallaAlarmaSonando> {
     _fallbackActivo = true;
     await _fallbackPlayer.setAsset(_assetFallback(widget.alarma.sonidoInterno));
     await _fallbackPlayer.play();
+    await _confirmarAudioFlutterListo();
     if (mounted) setState(() {});
   }
 
+  Future<void> _confirmarAudioFlutterListo() async {
+    if (_audioFlutterConfirmado) return;
+    _audioFlutterConfirmado = true;
+    await context.read<EstadoAlarmas>().android.confirmarAudioFlutter(
+      widget.alarma.id,
+    );
+  }
+
   Future<void> _detener() async {
     final radio = context.read<EstadoRadio>();
     final alarmas = context.read<EstadoAlarmas>();