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.

android/app/src/main/res/drawable/ic_auto_eq_off.xml

@@ -0,0 +1,3 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android" android:width="24dp" android:height="24dp" android:viewportWidth="24" android:viewportHeight="24">
+  <path android:fillColor="#FFFFFF" android:pathData="M3,5L21,5L21,7L3,7Z M14,3L17,3L17,9L14,9Z M3,11L21,11L21,13L3,13Z M7,9L10,9L10,15L7,15Z M3,17L21,17L21,19L3,19Z M17,15L20,15L20,21L17,21Z M2,20L4,22L22,4L20,2Z" />
+</vector>

android/app/src/main/res/drawable/ic_auto_eq_on.xml

@@ -0,0 +1,3 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android" android:width="24dp" android:height="24dp" android:viewportWidth="24" android:viewportHeight="24">
+  <path android:fillColor="#FFFFFF" android:pathData="M3,5L21,5L21,7L3,7Z M14,3L17,3L17,9L14,9Z M3,11L21,11L21,13L3,13Z M7,9L10,9L10,15L7,15Z M3,17L21,17L21,19L3,19Z M17,15L20,15L20,21L17,21Z" />
+</vector>

android/app/src/main/res/drawable/ic_auto_eq_preset.xml

@@ -0,0 +1,3 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android" android:width="24dp" android:height="24dp" android:viewportWidth="24" android:viewportHeight="24">
+  <path android:fillColor="#FFFFFF" android:pathData="M2,14L4,14L4,18L2,18Z M6,6L8,6L8,18L6,18Z M10,10L12,10L12,18L10,18Z M14,6L14,18L22,12Z" />
+</vector>

lib/servicios/servicio_audio.dart

@@ -154,12 +154,23 @@ String nombrePresetVisible(AppLocalizations l10n, String nombre) {
 /// screen (Design "EQ custom actions", item 4) — deliberately just 2: an
 /// on/off toggle plus a cycling-preset action, NOT one action per preset,
 /// since Android Auto only surfaces a limited number of custom actions.
+/// Folding "off" into the preset cycle (one button walking
+/// off → preset 1 → preset 2 → ... → preset 6 → off) was considered and
+/// REJECTED: with 6 presets that can take up to 6 taps to switch the EQ
+/// off while driving, which is worse for a driver than a dedicated one-tap
+/// toggle. Do not "simplify" this back down to a single action.
 /// Empty when [disponible] is false (gate on EQ availability, mirrors the
 /// existing `debeReaplicarEcualizador`/`_eqDisponible` gate) — a device
 /// without the native Equalizer effect gets no EQ actions at all, not
-/// broken ones. Reuses the SAME bundled `ic_stat_pluriwave` drawable the
-/// notification's own status-bar icon already uses (an equalizer-bars
-/// glyph) — zero new native assets. Pure, no handler dependency.
+/// broken ones.
+///
+/// On-device feedback follow-up: both actions used to reuse the SAME
+/// `ic_stat_pluriwave` drawable and were visually indistinguishable on a
+/// car head unit, which foregrounds the icon over the label. Each action
+/// now gets its own dedicated drawable (`ic_auto_eq_on`/`ic_auto_eq_off`/
+/// `ic_auto_eq_preset`), and the toggle's icon itself reflects [activo]
+/// (not just its label) so on/off is legible at a glance. Pure, no
+/// handler dependency.
 List<MediaControl> controlesEcualizadorPersonalizados({
   required bool disponible,
   required bool activo,
@@ -169,14 +180,16 @@ List<MediaControl> controlesEcualizadorPersonalizados({
   if (!disponible) return const [];
   return [
     MediaControl.custom(
-      androidIcon: 'drawable/ic_stat_pluriwave',
+      androidIcon: activo
+          ? 'drawable/ic_auto_eq_on'
+          : 'drawable/ic_auto_eq_off',
       label: activo
           ? l10n.eqCustomActionDisableLabel
           : l10n.eqCustomActionEnableLabel,
       name: accionEqToggle,
     ),
     MediaControl.custom(
-      androidIcon: 'drawable/ic_stat_pluriwave',
+      androidIcon: 'drawable/ic_auto_eq_preset',
       label: l10n.eqCustomActionPresetLabel(
         nombrePresetVisible(l10n, presetActual.nombre),
       ),

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/',
+            );
+          }
+        },
+      );
+    },
+  );
 }