feat(alarms): native reliability fixes and end-to-end snooze

- Use mediaPlayback|systemExempted FGS type with FOREGROUND_SERVICE_SYSTEM_EXEMPTED so alarms fire on Android 14+ (FOREGROUND_SERVICE_ALARM does not exist in the SDK)
- Deduplicate fire notifications: the foreground service FSI notification is the single owner; receiver path removed
- Notification channel v2 with alarm sound URI and USAGE_ALARM attributes, one-time guarded migration from legacy channels
- Pass fallback station through the MethodChannel (NativeAlarmSpec schemaVersion 3) with a three-stage audio chain: primary -> fallback station -> bundled WAV
- Native fade-in volume ramp honoring fadeInSegundos when the app is killed
- Request battery-optimization exemption once, tracked with a persisted asked-once flag
- Fix snooze end-to-end: native ACTION_SNOOZE now reports back to Flutter (snoozed event + cold-start sync), snooze anchor unified to occurrence+minutes on both sides, periodic recalc no longer erases an active snooze
- Add snooze buttons (3/5/10/custom) to the ringing screen with shared audio teardown
- Redesign ringing screen on PluriWaveScaffold with reduced-motion-aware entry animation (new PluriAnimate helper)
- Alarm editor: live next-trigger preview, searchable station pickers (primary and fallback), configurable snooze duration, volume floor down to 0
- New alarm strings localized across all 13 locales
- New unit/widget tests for the snooze flow, alarm bridge payloads, ringing screen and editor (77 tests green)
- SDD artifacts for the app-quality-and-native-alarms change (explore, proposal, spec, design, tasks, apply progress)

lib/app.dart

@@ -211,6 +211,11 @@ class _PaginaPrincipalState extends State<_PaginaPrincipal> {
   }
 
   Future<void> _abrirAlarmaSonando(EventoAlarmaAndroid evento) async {
+    if (evento.accion == EventoAlarmaAndroid.accionSnoozed) {
+      // EstadoAlarmas records native snoozes itself (Decision 2.1); there is
+      // nothing to open for this event.
+      return;
+    }
     final estado = context.read<EstadoAlarmas>();
     if (estado.alarmas.isEmpty) {
       await estado.cargarPersistidasSinRecalcular();
@@ -235,9 +240,7 @@ class _PaginaPrincipalState extends State<_PaginaPrincipal> {
       ScaffoldMessenger.of(context).showSnackBar(
         SnackBar(
           content: Text(
-            AppLocalizations.of(
-              context,
-            ).skipCurrentAlarmExecution(
+            AppLocalizations.of(context).skipCurrentAlarmExecution(
               localizedAlarmName(AppLocalizations.of(context), alarma.nombre),
             ),
           ),
@@ -438,10 +441,7 @@ class _PaginaPrincipalState extends State<_PaginaPrincipal> {
   }
 }
 
-String _formatearDuracionTimer(
-  AppLocalizations l10n,
-  Duration duracion,
-) {
+String _formatearDuracionTimer(AppLocalizations l10n, Duration duracion) {
   final horas = duracion.inHours;
   final minutos = duracion.inMinutes.remainder(60);
   final segundos = duracion.inSeconds.remainder(60);