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/pantallas/pantalla_alarma_sonando.dart

@@ -10,7 +10,10 @@ import '../l10n/display_names.dart';
 import '../l10n/gen/app_localizations.dart';
 import '../modelos/alarma_musical.dart';
 import '../servicios/servicio_audio.dart';
+import '../tema/pluri_animate.dart';
+import '../tema/pluriwave_theme.dart';
 import '../widgets/pluri_glass_surface.dart';
+import '../widgets/pluri_wave_scaffold.dart';
 
 class PantallaAlarmaSonando extends StatefulWidget {
   const PantallaAlarmaSonando({
@@ -129,19 +132,49 @@ class _PantallaAlarmaSonandoState extends State<PantallaAlarmaSonando> {
     );
   }
 
+  /// Shared local-audio teardown for stop and snooze (Design 2.3): the Dart
+  /// fallback player and fade timer MUST die before the alarm is re-programmed
+  /// natively, otherwise the local fallback keeps looping after snooze.
+  Future<void> _liberarAudioLocal() async {
+    _fallbackTimer?.cancel();
+    _fadeInTimer?.cancel();
+    // cancel() detiene la entrega de eventos de forma sincrona; no se espera
+    // su Future porque puede no resolverse hasta que el stream se cierre.
+    unawaited(_estadoSub?.cancel());
+    _estadoSub = null;
+    await _fallbackPlayer.stop();
+  }
+
   Future<void> _detener() async {
     final radio = context.read<EstadoRadio>();
     final alarmas = context.read<EstadoAlarmas>();
     final navigator = Navigator.of(context);
-    _fallbackTimer?.cancel();
-    _fadeInTimer?.cancel();
-    await _estadoSub?.cancel();
-    await _fallbackPlayer.stop();
+    await _liberarAudioLocal();
     await radio.audio.pausar();
     await alarmas.finalizarEjecucion(widget.alarma.id);
     if (mounted) navigator.pop();
   }
 
+  /// Flutter-first snooze (S2-R1): tears down local audio, then routes
+  /// through the canonical EstadoAlarmas.posponerAlarma, which hides the
+  /// native notification (same stop path as dismiss) and re-programs Android.
+  Future<void> _posponer(int minutos) async {
+    final radio = context.read<EstadoRadio>();
+    final alarmas = context.read<EstadoAlarmas>();
+    final navigator = Navigator.of(context);
+    await _liberarAudioLocal();
+    await radio.audio.pausar();
+    await alarmas.posponerAlarma(widget.alarma, minutos);
+    if (mounted) navigator.pop();
+  }
+
+  List<int> _opcionesSnooze() {
+    final opciones = <int>{3, 5, 10};
+    final propio = widget.alarma.snoozeMinutos;
+    if (propio > 0) opciones.add(propio);
+    return opciones.toList()..sort();
+  }
+
   @override
   void dispose() {
     _fallbackTimer?.cancel();
@@ -155,8 +188,12 @@ class _PantallaAlarmaSonandoState extends State<PantallaAlarmaSonando> {
   Widget build(BuildContext context) {
     final alarma = widget.alarma;
     final l10n = AppLocalizations.of(context);
-    return Scaffold(
-      backgroundColor: const Color(0xFF061722),
+    final tokens = context.pluriTokens;
+    // Cold-GPU note (Design 2.4): PluriGlassSurface uses a BackdropFilter and
+    // the first frame after a screen-off FSI wake can stutter. The blur sigma
+    // is capped here, and reduced-motion users skip the entry animation
+    // entirely via pluriFadeIn.
+    return PluriWaveScaffold(
       body: SafeArea(
         child: Padding(
           padding: const EdgeInsets.all(20),
@@ -164,7 +201,8 @@ class _PantallaAlarmaSonandoState extends State<PantallaAlarmaSonando> {
             child: PluriGlassSurface(
               borderRadius: BorderRadius.circular(32),
               padding: const EdgeInsets.all(24),
-              glowColor: const Color(0xFFFFB86B).withValues(alpha: 0.35),
+              blurSigma: 10,
+              glowColor: tokens.warmCoral.withValues(alpha: 0.35),
               child: Column(
                 mainAxisSize: MainAxisSize.min,
                 children: [
@@ -197,6 +235,25 @@ class _PantallaAlarmaSonandoState extends State<PantallaAlarmaSonando> {
                     textAlign: TextAlign.center,
                   ),
                   const SizedBox(height: 22),
+                  Text(
+                    l10n.snoozeAction,
+                    style: Theme.of(context).textTheme.labelLarge,
+                  ),
+                  const SizedBox(height: 8),
+                  Wrap(
+                    spacing: 8,
+                    runSpacing: 8,
+                    alignment: WrapAlignment.center,
+                    children: [
+                      for (final minutos in _opcionesSnooze())
+                        OutlinedButton.icon(
+                          onPressed: () => _posponer(minutos),
+                          icon: const Icon(Icons.snooze_rounded),
+                          label: Text(l10n.alarmSnoozeOptionLabel(minutos)),
+                        ),
+                    ],
+                  ),
+                  const SizedBox(height: 14),
                   FilledButton.icon(
                     onPressed: _detener,
                     icon: const Icon(Icons.stop_rounded),
@@ -204,7 +261,7 @@ class _PantallaAlarmaSonandoState extends State<PantallaAlarmaSonando> {
                   ),
                 ],
               ),
-            ),
+            ).pluriFadeIn(context),
           ),
         ),
       ),