feat(buscar): add discovery landing state, filter pills, counter, and sort

test/helpers/fakes.dart

@@ -9,6 +9,7 @@ import 'package:pluriwave/servicios/servicio_audio.dart';
 import 'package:pluriwave/servicios/servicio_dispositivo_audio.dart';
 import 'package:pluriwave/servicios/servicio_ecualizador.dart';
 import 'package:pluriwave/servicios/servicio_favoritos.dart';
+import 'package:pluriwave/servicios/servicio_grabacion_radio.dart';
 import 'package:pluriwave/servicios/servicio_radio.dart';
 
 class FakeServicioAudio extends ServicioAudio {
@@ -236,6 +237,7 @@ class FakeServicioRadio extends ServicioRadio {
   int obtenerPopularesCalls = 0;
   int obtenerTendenciasCalls = 0;
   int registrarClickCalls = 0;
+  int buscarCalls = 0;
   String? ultimoUuidClick;
 
   Exception _normalizarError(Object error) =>
@@ -279,6 +281,10 @@ class FakeServicioRadio extends ServicioRadio {
     int limit = 30,
     int offset = 0,
   }) async {
+    // WU6: counts calls so tests can assert a client-side re-sort does NOT
+    // trigger a new network request (`station-discovery-browse` spec,
+    // "Client-Side Search Sort Only").
+    buscarCalls++;
     return _busqueda.skip(offset).take(limit).toList();
   }
 
@@ -573,6 +579,28 @@ class FakeServicioDispositivoAudio extends ServicioDispositivoAudio {
   }
 }
 
+/// WU6: promoted from a local class in `pantalla_inicio_test.dart` to this
+/// shared helpers file, since `pantalla_buscar_test.dart` now needs the same
+/// inert stand-in — any widget test that constructs a full `EstadoRadio`
+/// must supply a `servicioGrabacion`, or the default REAL
+/// `ServicioGrabacionRadio` touches native platform channels and hangs
+/// inside `testWidgets()`.
+class FakeServicioGrabacionRadio extends ServicioGrabacionRadio {
+  final _controller = StreamController<EstadoGrabacionRadio>.broadcast();
+
+  @override
+  EstadoGrabacionRadio get estado => const EstadoGrabacionRadio.inactiva();
+
+  @override
+  Stream<EstadoGrabacionRadio> get estadoStream => _controller.stream;
+
+  @override
+  Future<void> inicializar() async {}
+
+  @override
+  Future<void> dispose() => _controller.close();
+}
+
 Emisora emisoraDemo({
   required String uuid,
   required String nombre,