feat(grabaciones): add recordings library screen

lib/servicios/servicio_grabacion_radio.dart

@@ -3,10 +3,12 @@ import 'dart:io';
 import 'dart:ui' show Locale;
 
 import 'package:http/http.dart' as http;
+import 'package:path/path.dart' as p;
 import 'package:path_provider/path_provider.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
 import '../l10n/gen/app_localizations.dart';
+import '../modelos/archivo_grabacion.dart';
 import '../modelos/emisora.dart';
 
 enum EstadoGrabacionRadioTipo {
@@ -173,6 +175,66 @@ class ServicioGrabacionRadio {
     _emitir(_estado);
   }
 
+  /// Lists the recording files currently on disk in the effective
+  /// directory (WU15, recordings-library spec "Browsable Recordings List").
+  /// Pure filesystem read — no audio decoding, no duration. Never throws: a
+  /// missing directory (never recorded yet) degrades to an empty list, not
+  /// an error, matching the spec's "No recordings (edge case)" scenario.
+  /// Sorted most-recent-first by last-modified time.
+  ///
+  /// Uses the SYNC `listSync`/`statSync` filesystem calls deliberately, not
+  /// `Directory.list()`'s async stream — the latter did not resolve inside
+  /// `flutter_test`'s fake-async zone in this sandbox (confirmed: a widget
+  /// test calling through to the stream-based version hung indefinitely,
+  /// while the sync calls resolve immediately), mirroring this project's
+  /// existing `Directory.systemTemp` async-hang precedent for a different
+  /// dart:io API shape.
+  Future<List<ArchivoGrabacion>> listarGrabaciones() async {
+    final ruta = await directorioEfectivo();
+    final directorio = Directory(ruta);
+    if (!directorio.existsSync()) return const [];
+
+    final archivos = <ArchivoGrabacion>[];
+    for (final entidad in directorio.listSync()) {
+      if (entidad is! File) continue;
+      final stat = entidad.statSync();
+      archivos.add(
+        ArchivoGrabacion(
+          ruta: entidad.path,
+          nombre: p.basenameWithoutExtension(entidad.path),
+          fecha: stat.modified,
+          tamanoBytes: stat.size,
+        ),
+      );
+    }
+    archivos.sort((a, b) => b.fecha.compareTo(a.fecha));
+    return archivos;
+  }
+
+  /// Deletes the recording at [ruta] (WU15, "Delete removes the file and
+  /// its row"). File-lifecycle management for a file this service already
+  /// created — not a new capability. A missing file is treated as
+  /// already-deleted, never an error.
+  Future<void> eliminarGrabacion(String ruta) async {
+    final archivo = File(ruta);
+    if (await archivo.exists()) {
+      await archivo.delete();
+    }
+  }
+
+  /// Renames the recording at [ruta] to [nuevoNombre], preserving its
+  /// original extension (WU15, "Rename updates the displayed name").
+  /// Returns the new full path.
+  Future<String> renombrarGrabacion(String ruta, String nuevoNombre) async {
+    final original = File(ruta);
+    final nuevaRuta = p.join(
+      p.dirname(ruta),
+      '$nuevoNombre${p.extension(ruta)}',
+    );
+    final renombrado = await original.rename(nuevaRuta);
+    return renombrado.path;
+  }
+
   Future<void> guardarMaxBytes(int bytes) async {
     if (bytes <= 0) {
       throw ArgumentError(_textos.recordingMaxSizeInvalidError);