fix(visualizador): add a discrete-bar rendering mode

Audit 1.7/2.5 (t4 lines 66-68, 120-122): the prototype draws 30
discrete bottom-anchored bars (radius 2, vertical gradient); the
build's VisualizadorAudio painted a single continuous oscilloscope
stroke, so its `barras: 30` parameter never produced bars.

Adds an opt-in `barrasDiscretas` mode (default false, byte-identical
continuous rendering preserved for any other caller) plus a
`gradienteFinAlpha` knob for the two screens' differing gradient
end-alpha (.3 vs .45). Wires it into the Escuchar hero and the full
player, correcting the player's bar count/height to match the
prototype (26->30 bars, 46->40px) at the same time.

test/pantallas/pantalla_inicio_test.dart

@@ -10,6 +10,7 @@ import 'package:pluriwave/estado/estado_radio.dart';
 import 'package:pluriwave/l10n/gen/app_localizations.dart';
 import 'package:pluriwave/modelos/emisora.dart';
 import 'package:pluriwave/pantallas/pantalla_inicio.dart';
+import 'package:pluriwave/widgets/visualizador_audio.dart';
 import 'package:provider/provider.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
@@ -208,6 +209,51 @@ void main() {
     );
   });
 
+  testWidgets(
+    'visual fidelity (audit 1.7): the hero visualizer renders 30 discrete '
+    'bars, not the continuous waveform stroke',
+    (tester) async {
+      // Item 16 is exactly the widget the audit warned about
+      // (visualizador_audio.dart:77, `_controller.repeat()`) — bounded pump
+      // only, never pumpAndSettle.
+      _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();
+      await tester.runAsync(() => estado.reproducir(sonando));
+
+      await tester.pumpWidget(
+        _conProviders(estado, _testApp(const PantallaInicio())),
+      );
+      await _pumpBounded(tester);
+
+      expect(
+        find.byKey(const Key('visualizador-barra-0')),
+        findsOneWidget,
+        reason: 'prototype t4 line 66-68: 30 discrete bottom-anchored bars',
+      );
+      expect(
+        find.descendant(
+          of: find.byType(VisualizadorAudio),
+          matching: find.byType(CustomPaint),
+        ),
+        findsNothing,
+      );
+    },
+  );
+
   testWidgets(
     'visual fidelity (audit 1.6): a station missing every meta field omits '
     'the line gracefully, no stray separators',

test/pantallas/pantalla_reproductor_test.dart

@@ -412,6 +412,35 @@ void main() {
         },
       );
 
+      testWidgets(
+        'visual fidelity (audit 2.5): the visualizer renders 30 discrete '
+        'bars, not the continuous waveform stroke',
+        (tester) async {
+          final estado = crearEstado();
+          addTearDown(estado.dispose);
+
+          await montarPantalla(tester, estado);
+
+          final visualizador = find.byKey(const Key('player-visualizer'));
+          expect(visualizador, findsOneWidget);
+          expect(
+            find.descendant(
+              of: visualizador,
+              matching: find.byKey(const Key('visualizador-barra-0')),
+            ),
+            findsOneWidget,
+            reason: 'prototype t4 line 120-122: 30 discrete bars',
+          );
+          expect(
+            find.descendant(
+              of: visualizador,
+              matching: find.byType(CustomPaint),
+            ),
+            findsNothing,
+          );
+        },
+      );
+
       testWidgets(
         'exactly 4 tool-tray tiles render: EQ propio, Grabar, sleep timer, Compartir',
         (tester) async {