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.dart

@@ -3367,6 +3367,54 @@ abstract class AppLocalizations {
   /// In es, this message translates to:
   /// **'Premium activo'**
   String get premiumActivo;
+
+  /// No description provided for @premiumHojaTitulo.
+  ///
+  /// In es, this message translates to:
+  /// **'Desbloquea PluriWave Premium'**
+  String get premiumHojaTitulo;
+
+  /// No description provided for @premiumBeneficioSinAnuncios.
+  ///
+  /// In es, this message translates to:
+  /// **'Sin publicidad en toda la app'**
+  String get premiumBeneficioSinAnuncios;
+
+  /// No description provided for @premiumBeneficioAndroidAuto.
+  ///
+  /// In es, this message translates to:
+  /// **'Android Auto'**
+  String get premiumBeneficioAndroidAuto;
+
+  /// No description provided for @premiumBeneficioGrabacion.
+  ///
+  /// In es, this message translates to:
+  /// **'Grabación de emisoras'**
+  String get premiumBeneficioGrabacion;
+
+  /// No description provided for @premiumBeneficioVacaciones.
+  ///
+  /// In es, this message translates to:
+  /// **'Rangos de vacaciones para las alarmas'**
+  String get premiumBeneficioVacaciones;
+
+  /// No description provided for @premiumBeneficioAlarmasIlimitadas.
+  ///
+  /// In es, this message translates to:
+  /// **'Alarmas ilimitadas (el plan gratuito permite hasta 5)'**
+  String get premiumBeneficioAlarmasIlimitadas;
+
+  /// No description provided for @premiumPagoUnico.
+  ///
+  /// In es, this message translates to:
+  /// **'Pago único, para siempre. No es una suscripción.'**
+  String get premiumPagoUnico;
+
+  /// No description provided for @premiumAhoraNo.
+  ///
+  /// In es, this message translates to:
+  /// **'Ahora no'**
+  String get premiumAhoraNo;
 }
 
 class _AppLocalizationsDelegate