fix(alarm): unfreeze snooze modal and add per-minute snooze countdown

The snooze button was fire-and-forget without error handling: if
posponerAlarma threw (e.g. native scheduleAlarm returns false on a
device without exact-alarm permission), _dismissScreen never ran. The
stuck modal also kept _alarmaSonandoActiva true, which made the next
ring get ignored. _posponer/_detener now dismiss in a finally and stop
audio defensively.

Add a native, AlarmManager-driven snooze countdown notification that
re-posts every minute ("Rings in N min", 3->2->1) while the engine is
dead. scheduleSpec drives scheduleSnoozeCountdown for snoozes (instead
of the 30-min pre-notice). Localized text and button labels travel
Dart->Kotlin as {minutes} templates, same pattern as preNoticeTemplate.

Notification actions: "snooze again" (snoozeAgain, anchored to now)
reports back via the existing snoozed event; "stop" (cancelSnooze)
records a handled occurrence for cold-start reconciliation and emits a
new snoozeCancelled event handled in EstadoAlarmas.

Adds snoozeCountdown/snoozeAgainAction keys across all 13 locales and a
test for the snoozeCancelled event. Kotlin changes are static-reviewed
only; no Android build environment available here.

lib/servicios/servicio_alarmas_android.dart

@@ -23,6 +23,10 @@ class EventoAlarmaAndroid {
   /// (notification "Posponer" while the app may be backgrounded/killed).
   static const accionSnoozed = 'snoozed';
 
+  /// Action reported when a pending snooze was cancelled natively from the
+  /// countdown notification ("Detener" while the app may be killed).
+  static const accionSnoozeCancelled = 'snoozeCancelled';
+
   final String alarmaId;
   final String titulo;
   final String accion;
@@ -183,6 +187,16 @@ class ServicioAlarmasAndroid implements PuertoAlarmasAndroid {
     );
   }
 
+  /// Same sentinel strategy as [_preNoticeTemplate], but for the snooze
+  /// countdown notification re-posted every minute while an alarm is snoozed.
+  static String _snoozeCountdownTemplate(AppLocalizations l10n) {
+    const sentinel = 42424242;
+    return l10n.snoozeCountdown(sentinel).replaceFirst(
+      sentinel.toString(),
+      '{minutes}',
+    );
+  }
+
   @override
   Stream<EventoAlarmaAndroid> get eventosAlarma => _eventosController.stream;
 
@@ -203,6 +217,9 @@ class ServicioAlarmasAndroid implements PuertoAlarmasAndroid {
       'id': alarma.id,
       'title': localizedAlarmName(_textos, alarma.nombre),
       'preNoticeTemplate': _preNoticeTemplate(_textos),
+      'snoozeCountdownTemplate': _snoozeCountdownTemplate(_textos),
+      'snoozeAgainLabel': _textos.snoozeAgainAction,
+      'snoozeStopLabel': _textos.stopAlarmAction,
       'triggerAtMillis': proxima.millisecondsSinceEpoch,
       'preNoticeAtMillis':
           alarma.snoozeHasta == null