feat(grabaciones): add recordings library screen

lib/modelos/archivo_grabacion.dart

@@ -0,0 +1,26 @@
+/// A single recorded audio file on disk, as listed by
+/// `ServicioGrabacionRadio.listarGrabaciones()` (WU15, recordings-library
+/// spec, "Browsable Recordings List"). Pure filesystem metadata only — no
+/// embedded-audio decoding here; duration is resolved separately and
+/// lazily by the screen's own playback abstraction, since decoding audio
+/// is not something this service conceptually does today.
+class ArchivoGrabacion {
+  const ArchivoGrabacion({
+    required this.ruta,
+    required this.nombre,
+    required this.fecha,
+    required this.tamanoBytes,
+  });
+
+  /// Full filesystem path — the identity used for playback, rename and
+  /// delete.
+  final String ruta;
+
+  /// Display name: the filename without its extension.
+  final String nombre;
+
+  /// Last-modified timestamp, used as the recording's date.
+  final DateTime fecha;
+
+  final int tamanoBytes;
+}