fix(ecualizador): header switch, banner radius, preset chips, glow thumb

Audit 11.1 (t4:566): the master enable switch moves to
PluriPushScaffold's header actions -- was the body's first
SwitchListTile row. Its realtime/pending explainer subtitle stays
behind as a plain caption so no information is lost.

Audit 11.2 (t4:571): explainer banner radius is 16 (a local one-off,
matching neither of the 3 named tokens), not radiusSm's 14.

Audit 11.3 (t4:574-577): preset chips are solid brand-teal with dark
text when active, listSurface + a faint border when not -- was
Material's own ChoiceChip theming (primaryContainer/grey).

Audit 11.5 (t4:585): band sliders use a new 20x20 _GlowSliderThumbShape
(brand-teal blurred glow + solid thumb), replacing the Material
default round thumb.

Audit 11.7 (t4:584): the dB label is brand teal at 90% alpha, not
liveGreen -- a leftover wrong colour family 11.6's slider-only fix
never touched.

Updated 2 pre-existing tests (pantalla_ajustes_ecualizador_test.dart,
pantalla_ajustes_test.dart) to locate the enable switch by key instead
of by the "Enable equalizer" text it no longer renders next to.

test/pantallas/ajustes/pantalla_ajustes_ecualizador_test.dart

@@ -9,6 +9,7 @@ import 'package:pluriwave/modelos/dispositivo_audio.dart';
 import 'package:pluriwave/modelos/emisora.dart';
 import 'package:pluriwave/modelos/preset_ecualizador.dart';
 import 'package:pluriwave/pantallas/ajustes/pantalla_ajustes_ecualizador.dart';
+import 'package:pluriwave/tema/pluriwave_tokens.dart';
 import 'package:pluriwave/widgets/ecualizador_widget.dart';
 import 'package:pluriwave/widgets/pluri_glass_surface.dart';
 import 'package:pluriwave/widgets/pluri_push_scaffold.dart';
@@ -119,9 +120,8 @@ void main() {
     expect((appBar.title as Text).data, equals('Equalizer'));
   });
 
-  testWidgets('moved control still responds: enable switch toggles activo', (
-    tester,
-  ) async {
+  testWidgets('moved control still responds: enable switch toggles activo '
+      '(audit 11.1: now in the header, t4 line 566)', (tester) async {
     _suppressListTileInkAssertion();
     final estado = await crearEstado();
     addTearDown(estado.dispose);
@@ -130,7 +130,7 @@ void main() {
     await tester.pumpAndSettle();
 
     final before = estado.ecualizador.activo;
-    await tester.tap(find.text('Enable equalizer'));
+    await tester.tap(find.byKey(const ValueKey('eq-master-switch')));
     await tester.pumpAndSettle();
 
     expect(estado.ecualizador.activo, equals(!before));
@@ -447,6 +447,74 @@ void main() {
       },
     );
 
+    testWidgets(
+      'visual fidelity (audit 11.1): the master switch is a header action, '
+      'not the body\'s first row (t4 line 566)',
+      (tester) async {
+        _suppressListTileInkAssertion();
+        final estado = await crearEstado();
+        addTearDown(estado.dispose);
+
+        await tester.pumpWidget(buildScreen(estado));
+        await tester.pumpAndSettle();
+
+        expect(
+          find.descendant(
+            of: find.byType(AppBar),
+            matching: find.byKey(const ValueKey('eq-master-switch')),
+          ),
+          findsOneWidget,
+          reason: 'the master switch lives in the AppBar, not the body',
+        );
+        expect(
+          find.descendant(
+            of: find.byType(ListView),
+            matching: find.byKey(const ValueKey('eq-master-switch')),
+          ),
+          findsNothing,
+        );
+      },
+    );
+
+    testWidgets(
+      'visual fidelity (audit 11.2): the explainer banner radius is 16, '
+      'not radiusSm\'s 14 (t4 line 571)',
+      (tester) async {
+        _suppressListTileInkAssertion();
+        final estado = await crearEstado();
+        addTearDown(estado.dispose);
+
+        await tester.pumpWidget(buildScreen(estado));
+        await tester.pumpAndSettle();
+
+        final banner = tester.widget<Container>(
+          find.byKey(const Key('eq-base-explainer-banner')),
+        );
+        final decoration = banner.decoration as BoxDecoration;
+        expect(
+          (decoration.borderRadius as BorderRadius).topLeft,
+          const Radius.circular(16),
+        );
+      },
+    );
+
+    testWidgets('visual fidelity (audit 11.3): the active preset chip is solid '
+        'brand teal with dark text (t4 lines 574-577)', (tester) async {
+      _suppressListTileInkAssertion();
+      final estado = await crearEstado();
+      addTearDown(estado.dispose);
+
+      await tester.pumpWidget(buildScreen(estado));
+      await tester.pumpAndSettle();
+
+      final chip = tester.widget<ChoiceChip>(
+        find.widgetWithText(ChoiceChip, 'Flat'),
+      );
+      expect(chip.selected, isTrue);
+      expect(chip.selectedColor, PluriWaveTokens.brand);
+      expect(chip.labelStyle?.color, const Color(0xFF062126));
+    });
+
     testWidgets(
       'Guardar como preset with a whitespace-only name shows the same validation message',
       (tester) async {

test/pantallas/pantalla_ajustes_test.dart

@@ -162,9 +162,10 @@ void main() {
       await pumpStable(tester);
 
       // Pushed, not index-switched: exactly one PluriPushScaffold now exists,
-      // and its moved control (the enable switch) is reachable.
+      // and its moved control (the enable switch, audit 11.1 -- now a
+      // header action, t4 line 566) is reachable.
       expect(find.byType(PluriPushScaffold), findsOneWidget);
-      expect(find.text('Enable equalizer'), findsOneWidget);
+      expect(find.byKey(const ValueKey('eq-master-switch')), findsOneWidget);
     });
 
     testWidgets('tapping the Orden de listas row pushes its detail screen', (