fix(auto): give the equalizer actions distinct, state-aware icons

On a car head unit the custom actions render icon-first, so two actions
sharing ic_stat_pluriwave were indistinguishable and the toggle gave no
sign of whether the equalizer was on.

Each action now has its own drawable, and the toggle swaps between
ic_auto_eq_on and ic_auto_eq_off so its state is legible at a glance.

test/servicios/servicio_audio_eq_custom_actions_test.dart

@@ -1,3 +1,4 @@
+import 'dart:io';
 import 'dart:ui' show Locale;
 
 import 'package:audio_service/audio_service.dart';
@@ -162,20 +163,53 @@ void main() {
       );
     });
 
-    test('both actions reuse the bundled notification drawable (zero new '
-        'native assets)', () {
-      final controles = controlesEcualizadorPersonalizados(
-        disponible: true,
-        activo: true,
-        presetActual: PresetEcualizador.flat,
-        l10n: l10n,
-      );
+    test(
+      'toggle icon reflects EQ state: ON uses ic_auto_eq_on, OFF uses '
+      'ic_auto_eq_off -- a car head unit foregrounds the icon over the '
+      'label, so the icon itself must change, not just the text',
+      () {
+        final activado = controlesEcualizadorPersonalizados(
+          disponible: true,
+          activo: true,
+          presetActual: PresetEcualizador.flat,
+          l10n: l10n,
+        ).firstWhere((c) => c.customAction?.name == accionEqToggle);
+        final desactivado = controlesEcualizadorPersonalizados(
+          disponible: true,
+          activo: false,
+          presetActual: PresetEcualizador.flat,
+          l10n: l10n,
+        ).firstWhere((c) => c.customAction?.name == accionEqToggle);
 
-      expect(
-        controles.every((c) => c.androidIcon == 'drawable/ic_stat_pluriwave'),
-        isTrue,
-      );
-    });
+        expect(activado.androidIcon, 'drawable/ic_auto_eq_on');
+        expect(desactivado.androidIcon, 'drawable/ic_auto_eq_off');
+      },
+    );
+
+    test(
+      'the toggle and the preset-cycle action never share an androidIcon, '
+      'in either EQ state -- this was the on-device bug: both buttons used '
+      'the same drawable and were visually indistinguishable',
+      () {
+        for (final activo in [true, false]) {
+          final controles = controlesEcualizadorPersonalizados(
+            disponible: true,
+            activo: activo,
+            presetActual: PresetEcualizador.flat,
+            l10n: l10n,
+          );
+          final iconos = controles.map((c) => c.androidIcon).toSet();
+
+          expect(
+            iconos.length,
+            controles.length,
+            reason:
+                'every custom action must have a distinct androidIcon '
+                '(activo=$activo)',
+          );
+        }
+      },
+    );
   });
 
   group('action name constants (item 4 — collision-free with car-tree ids)', () {
@@ -186,4 +220,37 @@ void main() {
       expect(accionEqToggle, isNot(equals(accionEqPresetSiguiente)));
     });
   });
+
+  group(
+    'equalizer drawable assets on disk (on-device feedback follow-up: the '
+    'two custom actions used to share one drawable and were visually '
+    'indistinguishable)',
+    () {
+      test(
+        'ic_auto_eq_on, ic_auto_eq_off and ic_auto_eq_preset all exist under '
+        'android/app/src/main/res/drawable/ -- a missing drawable is not a '
+        'build error, it silently renders blank/default on the head unit, '
+        'so this is the only safety net that would have caught the original '
+        'duplication',
+        () {
+          for (final nombre in [
+            'ic_auto_eq_on',
+            'ic_auto_eq_off',
+            'ic_auto_eq_preset',
+          ]) {
+            final archivo = File(
+              'android/app/src/main/res/drawable/$nombre.xml',
+            );
+            expect(
+              archivo.existsSync(),
+              isTrue,
+              reason:
+                  '$nombre.xml must exist under '
+                  'android/app/src/main/res/drawable/',
+            );
+          }
+        },
+      );
+    },
+  );
 }