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.

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),
       ),