feat(iap): add freemium unlock via one-time in-app purchase

Adds a permanent, non-consumable premium unlock (EstadoEntitlement +
PuertoCompras/ServicioComprasPlayBilling) that removes ads and unlocks
alarm vacations, alarms past a 5-alarm free cap, recording start, and
full Android Auto browsing. The phone equalizer stays free for everyone.

- Entitlement is prefs-backed (compra_premium_v1), fail-open, and
  resolvable headlessly via esPremiumPersistido() for the Android Auto
  audio handler, which registers before runApp.
- Android Auto reduced mode keeps the real root folder labels for free
  users; browsing into any of them (and playFromMediaId/playFromSearch/
  skipToNext/skipToPrevious) is blocked at the getChildren/servicio_audio
  choke points, with a locked "Función Premium" item as the backstop.
  Current-station play/pause/stop stays untouched. A free -> premium
  transition actively invalidates the head unit's cached browse tree.
- Ads (top banner + capped interstitial before adding a station or an
  alarm) are gated behind entitlement via ServicioAnuncios, using
  official Google test ad unit IDs pending AdMob provisioning.
- Alarm cap UX shows an explanatory message with a secondary unlock
  action rather than a bare paywall jump; existing data is grandfathered.
- 4 new localization keys translated across all 13 supported locales.

Co-located tests use strict TDD (RED test before implementation) for
every new pure-logic unit; full existing suite passes unchanged.

lib/estado/estado_alarmas.dart

@@ -9,15 +9,31 @@ import '../servicios/servicio_alarmas.dart';
 import '../servicios/servicio_alarmas_android.dart';
 import '../servicios/servicio_programacion_alarmas.dart';
 
+/// Distinct "limit reached" signal (Design ADR-5, freemium-gating spec
+/// "Alarm Count Cap At 5"): kept SEPARATE from [EstadoAlarmas.error], which
+/// stays reserved for native scheduling failures — overloading it would
+/// surface a free-tier limit as a scheduling failure in `app.dart`'s global
+/// snackbar path.
+enum ResultadoGuardarAlarma { guardada, limiteAlcanzado }
+
 class EstadoAlarmas extends ChangeNotifier {
   EstadoAlarmas({
     ServicioAlarmas? servicio,
     PuertoAlarmasAndroid? android,
     SharedPreferences? prefs,
     bool iniciarAutomaticamente = true,
+    // iap-freemium-unlock (Design ADR-3): entitlement query, mirroring
+    // `EstadoGrabacion`'s `emisoraActual` callback-injection shape rather
+    // than a direct `EstadoEntitlement` dependency (this notifier must stay
+    // constructible with zero widget-tree/Provider context). Defaults to
+    // "premium" (ungated) so every pre-existing test/call site that never
+    // wires entitlement keeps its exact previous behavior — production
+    // wiring in `app.dart` always passes the real callback.
+    bool Function()? esPremium,
   }) : servicio = servicio ?? ServicioAlarmas(prefs: prefs),
        android = android ?? ServicioAlarmasAndroid(),
-       _prefs = prefs {
+       _prefs = prefs,
+       _esPremium = esPremium ?? (() => true) {
     // Decision 2.1 (snooze sync): the native layer reports its own snoozes
     // back through alarmFired/snoozed; record them here so the Flutter
     // config stays the single source of truth.
@@ -32,8 +48,12 @@ class EstadoAlarmas extends ChangeNotifier {
   final ServicioAlarmas servicio;
   final PuertoAlarmasAndroid android;
   final SharedPreferences? _prefs;
+  final bool Function() _esPremium;
   static const _keyExencionBateriaSolicitada = 'bateria_exencion_solicitada';
 
+  /// Free-tier alarm cap (freemium-gating spec "Alarm Count Cap At 5").
+  static const maxAlarmasFree = 5;
+
   List<AlarmaMusical> _alarmas = [];
   List<RangoVacaciones> _vacaciones = [];
   List<ExcepcionAlarma> _excepciones = [];
@@ -101,7 +121,26 @@ class EstadoAlarmas extends ChangeNotifier {
     }
   }
 
-  Future<void> guardarAlarma(AlarmaMusical alarma) async {
+  /// Pure query (freemium-gating spec "Alarm Count Cap At 5"): whether a NEW
+  /// alarm may be created right now. Counts ALL alarms regardless of
+  /// `activa` (Spec "6th alarm creation is blocked" — "any enabled state").
+  /// Always `true` for premium (no cap). Editing an existing id is never
+  /// subject to this — see [guardarAlarma]'s own new-vs-edit check.
+  bool puedeCrearAlarma() => _esPremium() || _alarmas.length < maxAlarmasFree;
+
+  Future<ResultadoGuardarAlarma> guardarAlarma(AlarmaMusical alarma) async {
+    // Gate BEFORE any native scheduling attempt (freemium-gating spec "6th
+    // alarm creation is blocked": "no native scheduling is attempted").
+    // Editing an alarm that already exists (by id) is NEVER capped — only
+    // genuinely NEW creation counts against the limit (Spec "Editing an
+    // existing alarm is unaffected", grandfathering).
+    final esAlarmaNueva = !_alarmas.any((a) => a.id == alarma.id);
+    if (esAlarmaNueva && !puedeCrearAlarma()) {
+      debugPrint(
+        '[PluriWave][alarmas] guardar bloqueado por limite free id=${alarma.id}',
+      );
+      return ResultadoGuardarAlarma.limiteAlcanzado;
+    }
     debugPrint(
       '[PluriWave][alarmas] guardar id=${alarma.id} activa=${alarma.activa} hora=${alarma.hora}:${alarma.minuto} tipo=${alarma.tipoProgramacion.name}',
     );
@@ -125,6 +164,7 @@ class EstadoAlarmas extends ChangeNotifier {
       await _registrarFalloProgramacion(alarma.id);
     }
     notifyListeners();
+    return ResultadoGuardarAlarma.guardada;
   }
 
   Future<void> refrescarProgramacion() async {
@@ -507,9 +547,20 @@ class EstadoAlarmas extends ChangeNotifier {
     notifyListeners();
   }
 
-  Future<void> crearRangoVacaciones(RangoVacaciones rango) async {
+  /// Full premium gate (freemium-gating spec "Gated Feature Set (Exactly
+  /// 4)" — alarm vacations, unlike the alarm cap above, are gated entirely,
+  /// not counted): returns `false` without persisting anything when the
+  /// caller is free tier.
+  Future<bool> crearRangoVacaciones(RangoVacaciones rango) async {
+    if (!_esPremium()) {
+      debugPrint(
+        '[PluriWave][alarmas] crear vacaciones bloqueado (free) id=${rango.id}',
+      );
+      return false;
+    }
     final nuevos = [..._vacaciones, rango];
     await guardarVacaciones(nuevos);
+    return true;
   }
 
   Future<void> eliminarRangoVacaciones(String id) async {