fix(paywall): add dismiss controls and honest premium copy

The premium sheet had no close affordance or way to defer, and its
copy only said "Función Premium" without stating what it unlocks.
Adds a header close (X) button and a "not now" secondary action so
dismissal is never harder than purchasing, and replaces the bare
title with a concrete, honest breakdown of the 5 things premium
unlocks (no ads, Android Auto, station recording, alarm vacation
ranges, unlimited alarms) plus the one-time-purchase framing. The
phone equalizer is never listed, since it stays free for everyone.
New l10n keys added to all 13 locales.

lib/l10n/gen/app_localizations_es.dart

@@ -1881,4 +1881,31 @@ class AppLocalizationsEs extends AppLocalizations {
 
   @override
   String get premiumActivo => 'Premium activo';
+
+  @override
+  String get premiumHojaTitulo => 'Desbloquea PluriWave Premium';
+
+  @override
+  String get premiumBeneficioSinAnuncios => 'Sin publicidad en toda la app';
+
+  @override
+  String get premiumBeneficioAndroidAuto => 'Android Auto';
+
+  @override
+  String get premiumBeneficioGrabacion => 'Grabación de emisoras';
+
+  @override
+  String get premiumBeneficioVacaciones =>
+      'Rangos de vacaciones para las alarmas';
+
+  @override
+  String get premiumBeneficioAlarmasIlimitadas =>
+      'Alarmas ilimitadas (el plan gratuito permite hasta 5)';
+
+  @override
+  String get premiumPagoUnico =>
+      'Pago único, para siempre. No es una suscripción.';
+
+  @override
+  String get premiumAhoraNo => 'Ahora no';
 }