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.

lib/pantallas/pantalla_inicio.dart

@@ -291,6 +291,9 @@ class _EscucharHero extends StatelessWidget {
                         barras: 30,
                         altura: 26,
                         color: context.pluriTokens.liveGreen,
+                        // Audit 1.7 (t4 lines 66-68): 30 discrete
+                        // bottom-anchored bars, not a continuous stroke.
+                        barrasDiscretas: true,
                       ),
                     ],
                   ),

lib/pantallas/pantalla_reproductor.dart

@@ -152,6 +152,7 @@ class _PantallaReproductorState extends State<PantallaReproductor> {
               ).pluriFadeIn(context, delay: const Duration(milliseconds: 230)),
               const SizedBox(height: 14),
               PluriGlassSurface(
+                key: const Key('player-visualizer'),
                 borderRadius: BorderRadius.circular(tokens.radiusLg),
                 padding: const EdgeInsets.symmetric(
                   horizontal: 14,
@@ -161,9 +162,13 @@ class _PantallaReproductorState extends State<PantallaReproductor> {
                   estadoStream: estado.estadoStream,
                   androidAudioSessionIdStream:
                       estado.audio.androidAudioSessionIdStream,
-                  barras: 26,
+                  // Audit 2.5 (t4 lines 120-122): 30 discrete bars at 40px,
+                  // gradient ending at 45% alpha (not the hero's 30%).
+                  barras: 30,
                   color: tokens.warmCoral,
-                  altura: 46,
+                  altura: 40,
+                  barrasDiscretas: true,
+                  gradienteFinAlpha: 0.45,
                 ),
               ).pluriFadeIn(context, delay: const Duration(milliseconds: 270)),
               const SizedBox(height: 22),

lib/widgets/visualizador_audio.dart

@@ -20,6 +20,18 @@ class VisualizadorAudio extends StatefulWidget {
   final double altura;
   final double anchuraTotal;
 
+  /// Audit 1.7/2.5 (t4 lines 66-68, 120-122): the prototype draws `barras`
+  /// discrete bottom-anchored bars (radius 2, vertical gradient), not a
+  /// continuous oscilloscope stroke. Defaults to `false` so every OTHER
+  /// caller (if any is ever added) keeps the original `_WaveFlowPainter`
+  /// rendering unchanged.
+  final bool barrasDiscretas;
+
+  /// Alpha of the gradient's BOTTOM colour stop in discrete-bar mode. The
+  /// two current consumers disagree (Escuchar hero: `.3`, t4 line 67; full
+  /// player: `.45`, t4 line 121), so this is a parameter, not a constant.
+  final double gradienteFinAlpha;
+
   const VisualizadorAudio({
     super.key,
     required this.estadoStream,
@@ -28,6 +40,8 @@ class VisualizadorAudio extends StatefulWidget {
     this.color,
     this.altura = 48,
     this.anchuraTotal = double.infinity,
+    this.barrasDiscretas = false,
+    this.gradienteFinAlpha = 0.3,
   });
 
   @override
@@ -184,23 +198,79 @@ class _VisualizadorAudioState extends State<VisualizadorAudio>
   @override
   Widget build(BuildContext context) {
     final color = widget.color ?? Theme.of(context).colorScheme.primary;
-    final t = _controller.value * pi * 2;
     return SizedBox(
       height: widget.altura,
       width: widget.anchuraTotal,
       child: RepaintBoundary(
-        child: CustomPaint(
-          painter: _WaveFlowPainter(
-            color: color,
-            phase: t,
-            active: _activo,
-            waveform: _ondaVisual,
-          ),
-          child: const SizedBox.expand(),
-        ),
+        child:
+            widget.barrasDiscretas
+                ? _construirBarrasDiscretas(color)
+                : _construirOnda(color),
       ),
     );
   }
+
+  Widget _construirOnda(Color color) {
+    final t = _controller.value * pi * 2;
+    return CustomPaint(
+      painter: _WaveFlowPainter(
+        color: color,
+        phase: t,
+        active: _activo,
+        waveform: _ondaVisual,
+      ),
+      child: const SizedBox.expand(),
+    );
+  }
+
+  /// Audit 1.7/2.5 (t4 lines 66-68, 120-122): `barras` discrete,
+  /// bottom-anchored bars — radius 2, `gap:2px`, a top-to-bottom gradient
+  /// from [color] to `color@gradienteFinAlpha`. Reuses the SAME
+  /// `_ondaVisual`/`_ondaOrganica` amplitude source the continuous painter
+  /// already computes (real audio-session data when available, an organic
+  /// synthetic fallback otherwise) — only the paint strategy changes.
+  Widget _construirBarrasDiscretas(Color color) {
+    final valores = _valoresBarras();
+    final children = <Widget>[];
+    for (var i = 0; i < valores.length; i++) {
+      if (i > 0) children.add(const SizedBox(width: 2));
+      final valor = valores[i].clamp(0.08, 1.0);
+      children.add(
+        Expanded(
+          child: Align(
+            alignment: Alignment.bottomCenter,
+            child: Container(
+              key: ValueKey('visualizador-barra-$i'),
+              height: widget.altura * valor,
+              decoration: BoxDecoration(
+                borderRadius: BorderRadius.circular(2),
+                gradient: LinearGradient(
+                  begin: Alignment.topCenter,
+                  end: Alignment.bottomCenter,
+                  colors: [
+                    color,
+                    color.withValues(alpha: widget.gradienteFinAlpha),
+                  ],
+                ),
+              ),
+            ),
+          ),
+        ),
+      );
+    }
+    return Row(crossAxisAlignment: CrossAxisAlignment.end, children: children);
+  }
+
+  /// `_ondaVisual` is empty until the animation controller ticks at least
+  /// once (only happens once playback goes active, `_onEstado`'s
+  /// `_controller.repeat()`) — a discrete render before that must still show
+  /// `barras` resting bars, not zero, so it falls back to a flat, low
+  /// baseline of exactly [VisualizadorAudio.barras] values (clamped the same
+  /// way `_ondaOrganica` clamps its own count).
+  List<double> _valoresBarras() {
+    if (_ondaVisual.isNotEmpty) return _ondaVisual;
+    return List<double>.filled(widget.barras.clamp(8, 96), 0.12);
+  }
 }
 
 class _WaveFlowPainter extends CustomPainter {