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)

test/helpers/fakes.dart

@@ -18,6 +18,8 @@ class FakeServicioAudio extends ServicioAudio {
   final List<PresetEcualizador> presetsAplicados = [];
   final List<Emisora> emisorasReproducidas = [];
   final List<bool> cambiosEcualizadorActivo = [];
+  final List<double> volumenesAplicados = [];
+  int pausas = 0;
   Emisora? _emisoraActual;
   EstadoReproduccion _estadoActual = EstadoReproduccion.detenido;
 
@@ -46,6 +48,17 @@ class FakeServicioAudio extends ServicioAudio {
     emitirEstado(EstadoReproduccion.detenido);
   }
 
+  @override
+  Future<void> pausar() async {
+    pausas++;
+    emitirEstado(EstadoReproduccion.pausado);
+  }
+
+  @override
+  Future<void> setVolumen(double vol) async {
+    volumenesAplicados.add(vol);
+  }
+
   void emitirEstado(EstadoReproduccion estado) {
     _estadoActual = estado;
     _estadoController.add(estado);
@@ -116,7 +129,8 @@ class FakeServicioFavoritos extends ServicioFavoritos {
   }
 
   @override
-  Future<List<GrupoFavoritos>> obtenerGrupos() async => List.unmodifiable(_grupos);
+  Future<List<GrupoFavoritos>> obtenerGrupos() async =>
+      List.unmodifiable(_grupos);
 
   @override
   Future<GrupoFavoritos> crearGrupo(String nombre) async {
@@ -151,9 +165,10 @@ class FakeServicioFavoritos extends ServicioFavoritos {
 
   @override
   Future<void> asignarGrupo(String uuid, String grupoId) async {
-    final destino = _grupos.any((g) => g.id == grupoId)
-        ? grupoId
-        : GrupoFavoritos.sinAsignarId;
+    final destino =
+        _grupos.any((g) => g.id == grupoId)
+            ? grupoId
+            : GrupoFavoritos.sinAsignarId;
     final index = _favoritos.indexWhere((e) => e.uuid == uuid);
     if (index != -1) {
       _favoritos[index] = _favoritos[index].copyWith(grupoFavoritosId: destino);