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/l10n/gen/app_localizations_es.dart

@@ -1265,6 +1265,14 @@ class AppLocalizationsEs extends AppLocalizations {
     return 'Empieza en $minutes min';
   }
 
+  @override
+  String snoozeCountdown(int minutes) {
+    return 'Suena en $minutes min';
+  }
+
+  @override
+  String get snoozeAgainAction => 'Posponer otra vez';
+
   @override
   String get eqDeviceEditTitle => 'Editar dispositivo';