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/pantallas/ajustes/pantalla_ajustes_emisoras_personalizadas.dart

@@ -6,6 +6,7 @@ import '../../estado/estado_radio.dart';
 import '../../l10n/display_names.dart';
 import '../../l10n/gen/app_localizations.dart';
 import '../../modelos/emisora.dart';
+import '../../servicios/servicio_anuncios.dart';
 import '../../widgets/pluri_glass_surface.dart';
 import '../../widgets/pluri_layout.dart';
 import '../../widgets/pluri_push_scaffold.dart';
@@ -105,6 +106,11 @@ class _CuerpoEmisorasPersonalizadas extends StatelessWidget {
   }
 
   Future<void> _mostrarFormularioAnadir(BuildContext context) async {
+    // ad-display spec "Interstitial Before Manual Station Add" (design.md
+    // ADR-6): fires on the CTA tap, before the form even opens — a no-op
+    // for premium (ServicioAnuncios' own entitlement gate).
+    await context.read<ServicioAnuncios>().intentarInterstitial();
+    if (!context.mounted) return;
     await showModalBottomSheet(
       context: context,
       isScrollControlled: true,

lib/pantallas/pantalla_ajustes.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 
 import '../estado/estado_ecualizador.dart';
+import '../estado/estado_entitlement.dart';
 import '../estado/estado_grabacion.dart';
 import '../estado/estado_idioma.dart';
 import '../estado/estado_radio.dart';
@@ -10,6 +11,7 @@ import '../l10n/gen/app_localizations.dart';
 import '../modelos/archivo_grabacion.dart';
 import '../modelos/emisora.dart';
 import '../tema/pluriwave_tokens.dart';
+import '../widgets/hoja_premium.dart';
 import '../widgets/pluri_layout.dart';
 import '../widgets/pluri_push_scaffold.dart';
 import '../widgets/pluri_root_header.dart';
@@ -99,6 +101,9 @@ class _AjustesContent extends StatelessWidget {
     final idioma = context.select<EstadoIdioma, Locale?>(
       (e) => e.localeSeleccionado,
     );
+    final esPremium = context.select<EstadoEntitlement, bool>(
+      (e) => e.esPremium,
+    );
 
     return Column(
       children: [
@@ -256,6 +261,18 @@ class _AjustesContent extends StatelessWidget {
         GrupoAjustes(
           titulo: l10n.settingsGroupApplicationTitle,
           filas: [
+            // freemium-gating spec "Settings always shows a premium row":
+            // a persistent buy row (free tier) or a premium-active state
+            // with restore access (premium tier) — both open the same
+            // paywall sheet, which adapts its own body to the tier.
+            FilaAjuste(
+              key: const ValueKey('ajustes-fila-premium'),
+              icon: Icons.workspace_premium_rounded,
+              iconColor: PluriWaveTokens.brand,
+              titulo: l10n.funcionPremium,
+              valor: esPremium ? l10n.equalizerActive : null,
+              onTap: () => mostrarHojaPremium(context),
+            ),
             FilaAjuste(
               icon: Icons.language_rounded,
               titulo: l10n.languageSectionTitle,

lib/pantallas/pantalla_alarmas.dart

@@ -9,10 +9,12 @@ import '../l10n/app_localizations_ext.dart';
 import '../l10n/gen/app_localizations.dart';
 import '../modelos/alarma_musical.dart';
 import '../modelos/emisora.dart';
+import '../servicios/servicio_anuncios.dart';
 import '../servicios/servicio_programacion_alarmas.dart';
 import '../tema/pluriwave_theme.dart';
 import '../tema/pluriwave_tokens.dart';
 import '../widgets/editor_hora_inline.dart';
+import '../widgets/hoja_premium.dart';
 import '../widgets/pluri_glass_surface.dart';
 import '../widgets/pluri_layout.dart';
 import '../widgets/pluri_push_scaffold.dart';
@@ -105,6 +107,21 @@ class PantallaAlarmas extends StatelessWidget {
     BuildContext context, {
     AlarmaMusical? alarma,
   }) async {
+    // ADR-6 ordering (design.md): for a genuinely NEW alarm (no [alarma]),
+    // the cap-check + maybe-interstitial happen HERE, before the editor
+    // ever opens — "puedeCrearAlarma -> if false, show the limit message
+    // and no ad; if true, maybe-interstitial, then open the editor".
+    // Editing an existing alarm skips both checks entirely: it is never
+    // capped and never triggers the interstitial.
+    if (alarma == null) {
+      final estado = context.read<EstadoAlarmas>();
+      if (!estado.puedeCrearAlarma()) {
+        _mostrarLimiteAlarmas(context);
+        return;
+      }
+      await context.read<ServicioAnuncios>().intentarInterstitial();
+      if (!context.mounted) return;
+    }
     await showModalBottomSheet<void>(
       context: context,
       isScrollControlled: true,
@@ -113,6 +130,22 @@ class PantallaAlarmas extends StatelessWidget {
       builder: (_) => _EditorAlarmaSheet(alarma: alarma),
     );
   }
+
+  /// Freemium-gating spec "Alarm Cap UX Never Bare-Jumps To Paywall": an
+  /// explanatory message with a SECONDARY unlock action — never a direct
+  /// paywall navigation as the sole response to hitting the cap.
+  void _mostrarLimiteAlarmas(BuildContext context) {
+    final l10n = AppLocalizations.of(context);
+    ScaffoldMessenger.of(context).showSnackBar(
+      SnackBar(
+        content: Text(l10n.limiteAlarmasAlcanzado),
+        action: SnackBarAction(
+          label: l10n.desbloquearPremium,
+          onPressed: () => mostrarHojaPremium(context),
+        ),
+      ),
+    );
+  }
 }
 
 class _PanelProximaAlarma extends StatelessWidget {
@@ -1186,8 +1219,34 @@ class _EditorAlarmaSheetState extends State<_EditorAlarmaSheet> {
           sonidoInterno: _sonidoInterno,
           activa: true,
         );
-    await estado.guardarAlarma(alarma);
-    if (mounted) Navigator.pop(context);
+    // The cap-check + interstitial already ran in `PantallaAlarmas
+    // ._abrirEditor` BEFORE this sheet ever opened (ADR-6 ordering: "then
+    // open the editor"). This is only the defense-in-depth backstop against
+    // the state-layer choke point — e.g. a 2nd device created alarms while
+    // this sheet was open — the true authority is `guardarAlarma` itself.
+    final resultado = await estado.guardarAlarma(alarma);
+    if (!mounted) return;
+    if (resultado == ResultadoGuardarAlarma.limiteAlcanzado) {
+      _mostrarLimiteAlarmas(context);
+      return;
+    }
+    Navigator.pop(context);
+  }
+
+  /// Freemium-gating spec "Alarm Cap UX Never Bare-Jumps To Paywall": an
+  /// explanatory message with a SECONDARY unlock action — never a direct
+  /// paywall navigation as the sole response to hitting the cap.
+  void _mostrarLimiteAlarmas(BuildContext context) {
+    final l10n = AppLocalizations.of(context);
+    ScaffoldMessenger.of(context).showSnackBar(
+      SnackBar(
+        content: Text(l10n.limiteAlarmasAlcanzado),
+        action: SnackBarAction(
+          label: l10n.desbloquearPremium,
+          onPressed: () => mostrarHojaPremium(context),
+        ),
+      ),
+    );
   }
 
   List<Emisora> _favoritasConSeleccion(List<Emisora> favoritas) {

lib/pantallas/pantalla_favoritos.dart

@@ -6,6 +6,7 @@ import '../l10n/display_names.dart';
 import '../l10n/gen/app_localizations.dart';
 import '../modelos/emisora.dart';
 import '../modelos/grupo_favoritos.dart';
+import '../servicios/servicio_anuncios.dart';
 import '../tema/pluriwave_tokens.dart';
 import '../widgets/fila_emisora_plana.dart';
 import '../widgets/pluri_icon.dart';
@@ -38,6 +39,11 @@ class _PantallaFavoritosState extends State<PantallaFavoritos> {
   String? _grupoSeleccionadoId;
 
   Future<void> _abrirFormularioEmisoraPersonalizada() async {
+    // ad-display spec "Interstitial Before Manual Station Add" (design.md
+    // ADR-6): fires on the CTA tap, before the form even opens — a no-op
+    // for premium (ServicioAnuncios' own entitlement gate).
+    await context.read<ServicioAnuncios>().intentarInterstitial();
+    if (!mounted) return;
     await showModalBottomSheet(
       context: context,
       isScrollControlled: true,

lib/pantallas/pantalla_reproductor.dart

@@ -17,6 +17,7 @@ import '../tema/pluri_animate.dart';
 import '../tema/pluriwave_theme.dart';
 import '../tema/pluriwave_tokens.dart';
 import '../widgets/ecualizador_widget.dart';
+import '../widgets/hoja_premium.dart';
 import '../widgets/pluri_glass_surface.dart';
 import '../widgets/pluri_premium_widgets.dart';
 import '../widgets/pluri_push_scaffold.dart';
@@ -597,6 +598,28 @@ class _GrabacionWidget extends StatelessWidget {
     }
   }
 
+  /// Freemium gate choke point at the UI layer (freemium-gating spec "Free
+  /// user starts a new recording"): all 3 record-start call sites route
+  /// through here. [ctx] is the picker sheet/dialog's own (short-lived)
+  /// context — closed FIRST (matching the pre-existing pop-then-done shape).
+  /// [contextExterno] is the screen's own longer-lived context, used ONLY to
+  /// react to the AUTHORITATIVE [EstadoGrabacion.iniciar] result: a
+  /// free-tier block opens the paywall there instead of a plain error, since
+  /// [ctx] is already gone by then.
+  Future<void> _iniciarGrabacionYCerrar(
+    BuildContext ctx,
+    BuildContext contextExterno,
+    EstadoGrabacion grabacion, {
+    Duration? duracion,
+  }) async {
+    final resultado = await grabacion.iniciar(duracion: duracion);
+    if (ctx.mounted) Navigator.pop(ctx);
+    if (resultado == ResultadoIniciarGrabacion.requierePremium &&
+        contextExterno.mounted) {
+      await mostrarHojaPremium(contextExterno);
+    }
+  }
+
   void _mostrarDialogoGrabacion(BuildContext context) {
     final grabacion = context.read<EstadoGrabacion>();
     showModalBottomSheet(
@@ -626,10 +649,12 @@ class _GrabacionWidget extends StatelessWidget {
                           size: 18,
                         ),
                         label: Text(AppLocalizations.of(ctx).indefiniteOption),
-                        onPressed: () {
-                          grabacion.iniciar();
-                          Navigator.pop(ctx);
-                        },
+                        onPressed:
+                            () => _iniciarGrabacionYCerrar(
+                              ctx,
+                              context,
+                              grabacion,
+                            ),
                       ),
                       for (final opcion in _opciones)
                         ActionChip(
@@ -642,10 +667,13 @@ class _GrabacionWidget extends StatelessWidget {
                                   opcion.duracion.inSeconds,
                                 ),
                           ),
-                          onPressed: () {
-                            grabacion.iniciar(duracion: opcion.duracion);
-                            Navigator.pop(ctx);
-                          },
+                          onPressed:
+                              () => _iniciarGrabacionYCerrar(
+                                ctx,
+                                context,
+                                grabacion,
+                                duracion: opcion.duracion,
+                              ),
                         ),
                       ActionChip(
                         avatar: const Icon(Icons.tune_rounded, size: 18),
@@ -718,8 +746,12 @@ class _GrabacionWidget extends StatelessWidget {
                     seconds: segundos,
                   );
                   if (duracion <= Duration.zero) return;
-                  grabacion.iniciar(duracion: duracion);
-                  Navigator.pop(ctx);
+                  _iniciarGrabacionYCerrar(
+                    ctx,
+                    context,
+                    grabacion,
+                    duracion: duracion,
+                  );
                 },
                 child: Text(AppLocalizations.of(ctx).recordAction),
               ),

lib/pantallas/pantalla_vacaciones.dart

@@ -8,6 +8,7 @@ import '../l10n/gen/app_localizations.dart';
 import '../modelos/alarma_musical.dart';
 import '../tema/pluriwave_theme.dart';
 import '../tema/pluriwave_tokens.dart';
+import '../widgets/hoja_premium.dart';
 import '../widgets/pluri_glass_surface.dart';
 import '../widgets/pluri_layout.dart';
 import '../widgets/pluri_push_scaffold.dart';
@@ -927,7 +928,14 @@ class _EditorVacacionesSheetState extends State<_EditorVacacionesSheet> {
         fin: _fin,
         nombre: nombre,
       );
-      await estado.crearRangoVacaciones(rango);
+      // freemium-gating spec "Gated Feature Set": vacation creation is
+      // fully gated (unlike the alarm cap, there is no free allowance) —
+      // `crearRangoVacaciones` is the authoritative choke point.
+      final creada = await estado.crearRangoVacaciones(rango);
+      if (!creada) {
+        if (mounted) await mostrarHojaPremium(context);
+        return;
+      }
     }
     if (mounted) Navigator.pop(context);
   }