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_en.dart

@@ -1867,4 +1867,30 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String get premiumActivo => 'Premium active';
+
+  @override
+  String get premiumHojaTitulo => 'Unlock PluriWave Premium';
+
+  @override
+  String get premiumBeneficioSinAnuncios => 'No ads anywhere in the app';
+
+  @override
+  String get premiumBeneficioAndroidAuto => 'Android Auto';
+
+  @override
+  String get premiumBeneficioGrabacion => 'Station recording';
+
+  @override
+  String get premiumBeneficioVacaciones => 'Vacation ranges for alarms';
+
+  @override
+  String get premiumBeneficioAlarmasIlimitadas =>
+      'Unlimited alarms (the free plan allows up to 5)';
+
+  @override
+  String get premiumPagoUnico =>
+      'One-time purchase, forever. Not a subscription.';
+
+  @override
+  String get premiumAhoraNo => 'Not now';
 }