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/main.dart

@@ -5,6 +5,7 @@ import 'dart:ui' as ui;
 import 'package:audio_service/audio_service.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
+import 'package:google_mobile_ads/google_mobile_ads.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 import 'app.dart';
 import 'servicios/arranque_audio.dart';
@@ -12,6 +13,7 @@ import 'servicios/musica_local_auto.dart';
 import 'servicios/navegacion_auto.dart';
 import 'servicios/servicio_audio.dart';
 import 'servicios/servicio_audio_session.dart';
+import 'servicios/servicio_compras.dart';
 import 'servicios/servicio_presets_personalizados.dart';
 import 'tema/pluriwave_tokens.dart';
 
@@ -104,6 +106,13 @@ Future<void> main() async {
   // actually take effect anyway.
   unawaited(aplicarPoliticaOrientacion());
 
+  // iap-freemium-unlock: neither SDK init call blocks `runApp` — a purchase
+  // stream subscription and an ad-SDK warm-up are both safe to finish late
+  // (mirrors `aplicarPoliticaOrientacion`'s "cosmetic, never gates startup"
+  // rule immediately above).
+  unawaited(MobileAds.instance.initialize());
+  final compras = ServicioComprasPlayBilling();
+
   // S3-R4: single SharedPreferences instance resolved once at startup and
   // injected into every state/service below.
   final prefs = await SharedPreferences.getInstance();
@@ -155,7 +164,7 @@ Future<void> main() async {
   }
 
   Widget construirApp() => _OrientacionResponsiveApp(
-    child: PluriWaveApp(prefs: prefs, fuenteAuto: fuenteAuto),
+    child: PluriWaveApp(prefs: prefs, fuenteAuto: fuenteAuto, compras: compras),
   );
 
   final resultado = await esperarArranqueAudio(handlerFuturo);