fix(escuchar): restore the prototype's 132px hero artwork

Audit 1.3: the hero art shipped at 84 where the prototype draws 132
(t4 line 56), with a 24 corner radius rather than the shared radiusMd.

Adds a dimension guard. Every existing test on this screen asserts
behaviour only, which is why an artwork 36% too small went unnoticed.

lib/pantallas/pantalla_inicio.dart

@@ -307,12 +307,15 @@ class _ArteEscuchar extends StatelessWidget {
 
   final Emisora emisora;
 
-  static const _lado = 84.0;
+  /// Audit 1.3: the prototype's Escuchar hero art is 132 (t4 line 56), and
+  /// its corner radius is 24 rather than the shared `radiusMd`.
+  static const _lado = 132.0;
+  static const _radio = 24.0;
 
   @override
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
-    final radius = BorderRadius.circular(context.pluriTokens.radiusMd);
+    final radius = BorderRadius.circular(_radio);
     return PluriGlassSurface(
       padding: EdgeInsets.zero,
       borderRadius: radius,

test/pantallas/pantalla_inicio_test.dart

@@ -122,6 +122,48 @@ void main() {
       reason: 'switches tabs — must NOT push a new route',
     );
   });
+
+  testWidgets('visual fidelity (audit 1.3): the hero art is 132 square', (
+    tester,
+  ) async {
+    // The redesign shipped this at 84 — the prototype draws 132 (t4 line
+    // 56). Nothing caught it because every existing test here asserts
+    // behaviour, never dimensions. This is the guard that would have.
+    _setLargeSurfaceSize(tester);
+    final favoritos = FakeServicioFavoritos();
+    final estado = EstadoRadio(
+      audio: FakeServicioAudio(),
+      favoritos: favoritos,
+      radio: FakeServicioRadio(),
+      servicioEcualizador: FakeServicioEcualizador(),
+      servicioGrabacion: FakeServicioGrabacionRadio(),
+      resolverArchivoCustom: _archivoCustomVacio,
+      iniciarAutomaticamente: false,
+    );
+    addTearDown(estado.dispose);
+    await tester.runAsync(estado.inicializar);
+    final sonando = emisoraDemo(uuid: 'f1', nombre: 'Favorita Uno');
+    await favoritos.agregar(sonando);
+    await estado.cargarFavoritos();
+    // The hero only renders when a station is active — `emisoraActual` is
+    // what gates it. Without this the assertion below passes vacuously.
+    await tester.runAsync(() => estado.reproducir(sonando));
+
+    await tester.pumpWidget(
+      _conProviders(estado, _testApp(const PantallaInicio())),
+    );
+    await _pumpBounded(tester);
+
+    final cuadrados = tester
+        .widgetList<SizedBox>(find.byType(SizedBox))
+        .where((s) => s.width == 132 && s.height == 132);
+
+    expect(
+      cuadrados,
+      isNotEmpty,
+      reason: 'prototype t4 line 56 sizes the Escuchar hero artwork at 132',
+    );
+  });
 }
 
 /// Mirrors the app.dart wiring: EstadoRadio owns the domain notifiers and