fix(auto): remove the preset-cycling custom action, superseded by folder

The equalizer's preset-cycling custom action (eq_preset_siguiente) and
its ic_auto_eq_preset drawable are no longer needed now that the
"Ecualizador" folder lists all six presets directly: the folder replaces
what the cycle action did, and this frees a scarce Android Auto custom
action slot.

The on/off toggle is now the equalizer's only custom action.

lib/servicios/servicio_audio.dart

@@ -111,7 +111,6 @@ Emisora emisoraDesdeMediaItem(MediaItem mediaItem) {
 /// `MediaControl`/`customAction` namespace, never compared against a
 /// media id).
 const accionEqToggle = 'eq_toggle';
-const accionEqPresetSiguiente = 'eq_preset_siguiente';
 
 /// Advances to the NEXT factory preset after [actual] in [presets] order
 /// (Design "EQ custom actions — cycling presets", item 4): wraps around
@@ -154,30 +153,33 @@ String nombrePresetVisible(AppLocalizations l10n, String nombre) {
 }
 
 /// Builds the equalizer's custom-action `MediaControl`s for the now-playing
-/// 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.
+/// screen (decision `auto/ecualizador-diseno`) — exactly 1: an on/off
+/// toggle. The previous design paired this with a SECOND action that cycled
+/// through the six factory presets; that action is REMOVED. On-device
+/// feedback: many head units render custom actions icon-first, so two
+/// static, non-parametrized glyphs sitting side by side looked identical/
+/// dead even though the toggle's own icon DID change and the cycle action
+/// DID work — a monochrome icon simply cannot legibly encode "which of six
+/// presets" the way a browsable list's text rows can. Preset selection now
+/// lives in the "Ecualizador" browsable folder instead (see
+/// [itemsEcualizadorAuto]), which also frees this scarce custom-action
+/// slot. Do NOT re-add a preset-cycling custom action; extend the folder
+/// instead.
 /// 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.
 ///
-/// 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
+/// On-device feedback follow-up: this action used to reuse the SAME
+/// `ic_stat_pluriwave` drawable as everything else and was visually
+/// indistinguishable on a car head unit, which foregrounds the icon over
+/// the label. It now gets its own dedicated drawables
+/// (`ic_auto_eq_on`/`ic_auto_eq_off`), and the 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,
-  required PresetEcualizador presetActual,
   required AppLocalizations l10n,
 }) {
   if (!disponible) return const [];
@@ -191,13 +193,6 @@ List<MediaControl> controlesEcualizadorPersonalizados({
               : l10n.eqCustomActionEnableLabel,
       name: accionEqToggle,
     ),
-    MediaControl.custom(
-      androidIcon: 'drawable/ic_auto_eq_preset',
-      label: l10n.eqCustomActionPresetLabel(
-        nombrePresetVisible(l10n, presetActual.nombre),
-      ),
-      name: accionEqPresetSiguiente,
-    ),
   ];
 }
 
@@ -568,7 +563,6 @@ class PluriWaveAudioHandler extends BaseAudioHandler
       controlesEcualizadorPersonalizados(
         disponible: _eqDisponible,
         activo: _ecualizadorActivo,
-        presetActual: _presetActual,
         l10n: _textos,
       );
 
@@ -1176,14 +1170,17 @@ class PluriWaveAudioHandler extends BaseAudioHandler
     await _reproducirEntradaCola(anterior.actual);
   }
 
-  /// Dispatches the equalizer's 2 custom actions (item 4, Design "EQ custom
-  /// actions"): `accionEqToggle` flips on/off, `accionEqPresetSiguiente`
-  /// cycles to the next factory preset. Both delegate to the existing
-  /// [setEcualizadorActivo]/[aplicarPreset] — the SAME entry points the
+  /// Dispatches the equalizer's only custom action (decision
+  /// `auto/ecualizador-diseno`): `accionEqToggle` flips on/off, delegating
+  /// to the existing [setEcualizadorActivo] — the SAME entry point the
   /// phone settings screen uses via `EstadoEcualizador` — so a car tap and a
-  /// phone tap have identical effects and both refresh the custom action's
-  /// label via `_actualizarControlesEq()` (already wired into those two
-  /// methods). Any other [name] is a no-op — never throws.
+  /// phone tap have identical effects and both refresh the action's label
+  /// via `_actualizarControlesEq()` (already wired into that method). The
+  /// preset-cycling action that used to live here is REMOVED — preset
+  /// selection now goes through the "Ecualizador" browsable folder (see
+  /// `seleccionarPresetEqPorMediaId` in `navegacion_auto.dart`, dispatched
+  /// from [playFromMediaId] below). Any other [name] is a no-op — never
+  /// throws.
   @override
   Future<dynamic> customAction(
     String name, [
@@ -1192,8 +1189,6 @@ class PluriWaveAudioHandler extends BaseAudioHandler
     switch (name) {
       case accionEqToggle:
         await setEcualizadorActivo(!_ecualizadorActivo);
-      case accionEqPresetSiguiente:
-        await aplicarPreset(presetSiguiente(_presetActual));
     }
   }