fix(alarm): fail-safe alarm system overhaul (SDD alarm-system-overhaul, slice A)

Root-cause fix for the unstoppable-alarm incident (alarm rang 15 minutes,
only uninstall silenced it) plus systematic hardening of every stop path.

Native (Kotlin):
- Verified stop: stopActiveAlarm now derives its result from the real
  post-teardown state (companion instance + synchronous stopEverything +
  activeRingingId check) instead of reporting unconditional success.
- Atomic teardown: every stop path (stop action, notification button,
  snooze, missed, onDestroy, startForeground failure) funnels through one
  stopEverything() covering audio, wakelock, notification, foreground
  state and firing-record cleanup; player.release() guarded.
- Bounded ringing: 10-minute auto-silence armed via AlarmManager fires a
  FIRED->MISSED transition with a localized missed-alarm notification;
  repeating alarms keep their native rearm, deleted alarms never produce
  ghost MISSED notifications.
- Durable firing record with onStartCommand re-validation (resurrection
  guard) and boot-time stale cleanup; firing records cleared on every
  refuse/mismatch/cancel path.
- New notification-only dismissal channel (dismissAlarmNotificationOnly)
  so UI-level dedup can never kill a live ring's audio.

Flutter (Dart):
- Stop/disable/edit/delete of a ringing alarm always attempt to silence
  it; on native-query failure the stop falls back toward silence via the
  id-scoped legacy stop.
- Verified-stop results surface failures: the ringing screen keeps
  dismiss-by-design on success, but on a verified failure it stays up
  with a persistent force-stop banner (guarded against double-dismiss)
  and auto-dismisses if the ring ends externally (missed/notification).
- Missed events sync alarm bookkeeping without opening the ringing UI.
- 4 new l10n keys translated across all 13 locales (ARB guard green).

550 tests green, analyzer clean. Reviewed in 3 adversarial 4-lens rounds
(2 deterministic + 1 refuter-corroborated critical fixed); formal
gentle-ai receipt waived by maintainer authorization (correction scope
legitimately exceeded the frozen genesis paths). On-device QA checklist
in openspec/changes/alarm-system-overhaul/tasks.md pending before
archive.

lib/app.dart

@@ -281,6 +281,12 @@ class _PaginaPrincipalState extends State<_PaginaPrincipal>
       // nothing to open for this event.
       return;
     }
+    if (evento.accion == EventoAlarmaAndroid.accionMissed) {
+      // EstadoAlarmas' own native-event listener already recorded this
+      // transition (RES-1); the ring already ended, so opening the ringing
+      // screen here would only show a stale, already-silent alarm.
+      return;
+    }
     final estado = context.read<EstadoAlarmas>();
     if (estado.alarmas.isEmpty) {
       await estado.cargarPersistidasSinRecalcular();
@@ -361,15 +367,14 @@ class _PaginaPrincipalState extends State<_PaginaPrincipal>
       );
       // A duplicate delivery of the SAME ring's own fire event (the live
       // eventosAlarma stream and the one-shot obtenerEventoInicial() read
-      // the same native event and can both reach here) must be a no-op:
-      // ocultarNotificacionAlarma -> dismissAlarmNotification unconditionally
-      // stops PluriWaveAlarmService for that id on the native side, which
-      // would tear down the currently-ringing service and undo the
-      // ring-scoped media-volume override long before the real handoff.
-      // Only hide the notification when a genuinely DIFFERENT alarm fired
-      // while this one is active (single-ring-at-a-time by design).
+      // the same native event and can both reach here) must be a no-op.
+      // When a genuinely DIFFERENT alarm fired while this one is active
+      // (single-ring-at-a-time by design), hide ONLY its notification
+      // (RES-1): ocultarNotificacionAlarma -> dismissAlarmNotification
+      // unconditionally stops PluriWaveAlarmService, which would silently
+      // kill the OTHER alarm's ring if it is the one genuinely sounding.
       if (alarma.id != _alarmaSonandoId) {
-        await alarmas.android.ocultarNotificacionAlarma(alarma.id);
+        await alarmas.android.ocultarSoloNotificacion(alarma.id);
       }
       return;
     }