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/servicios/servicio_alarmas.dart

@@ -123,9 +123,7 @@ class ServicioAlarmas {
   ) async {
     final config = await cargar();
     final normalizadas =
-        vacaciones
-            .map((v) => v.normalizado())
-            .toList()
+        vacaciones.map((v) => v.normalizado()).toList()
           ..sort((a, b) => a.inicioDia.compareTo(b.inicioDia));
     final alarmas =
         config.alarmas
@@ -147,9 +145,10 @@ class ServicioAlarmas {
   }) {
     final rango = RangoVacaciones(
       id: _uuid.v4(),
-      nombre: (nombre == null || nombre.trim().isEmpty)
-          ? 'Vacaciones'
-          : nombre.trim(),
+      nombre:
+          (nombre == null || nombre.trim().isEmpty)
+              ? 'Vacaciones'
+              : nombre.trim(),
       inicio: inicio,
       fin: fin,
     );
@@ -259,7 +258,17 @@ class ServicioAlarmas {
     DateTime ejecucion,
     int minutos,
   ) async {
-    final snoozeHasta = _programacion.calcularSnooze(_reloj(), minutos);
+    // Unified snooze anchor (Design 2.2): occurrence + minutes, clamped to
+    // now + minutes when the target already passed. Matches the native
+    // AlarmScheduler.snooze/postponeNext semantics so both layers always
+    // land on the same re-fire time.
+    final seguros = minutos.clamp(1, 120);
+    final objetivo = ejecucion.add(Duration(minutes: seguros));
+    final ahora = _reloj();
+    final snoozeHasta =
+        objetivo.isAfter(ahora)
+            ? objetivo
+            : ahora.add(Duration(minutes: seguros));
     return posponerEjecucionHasta(alarmaId, ejecucion, snoozeHasta);
   }
 
@@ -381,8 +390,12 @@ class ServicioAlarmas {
     List<ExcepcionAlarma> excepciones,
   ) {
     final ahora = _reloj();
+    // S2-R5: a disabled alarm must not keep a pending snooze; clearing it
+    // here guarantees the snoozed occurrence dies with the alarm.
     final snoozeActivo =
-        alarma.snoozeHasta != null && alarma.snoozeHasta!.isAfter(ahora);
+        alarma.activa &&
+        alarma.snoozeHasta != null &&
+        alarma.snoozeHasta!.isAfter(ahora);
     final proxima = _programacion.calcularProxima(
       alarma: alarma,
       desde: ahora,