feat(auto): add an Ecualizador browsable folder with preset selection

On-device feedback showed the equalizer's preset-cycling custom action
looked dead: many head units render custom actions icon-first, and a
monochrome icon cannot legibly encode "which of six presets" the way a
browsable list's text rows can.

This adds an "Ecualizador" folder to the car's browse tree, listing
"Desactivar" first, then the six factory presets by name, with the
currently-active one marked. Selecting a preset routes through the same
playFromMediaId seam every other browse-tree leaf already uses; picking
a preset while the equalizer is off turns it on and applies that preset.

Supersedes the earlier "no equalizer folder" rule (commit 2403da3),
which predated this feedback -- see decision auto/ecualizador-diseno.

The preset-cycling custom action still coexists with the folder in this
commit; it is removed in the next one.

lib/l10n/gen/app_localizations.dart

@@ -3068,6 +3068,12 @@ abstract class AppLocalizations {
   /// **'Preset: {preset}'**
   String eqCustomActionPresetLabel(String preset);
 
+  /// No description provided for @autoEqDisableOption.
+  ///
+  /// In es, this message translates to:
+  /// **'Desactivar'**
+  String get autoEqDisableOption;
+
   /// No description provided for @alarmCardVacationPausedBadge.
   ///
   /// In es, this message translates to:

lib/l10n/gen/app_localizations_ar.dart

@@ -1688,6 +1688,9 @@ class AppLocalizationsAr extends AppLocalizations {
     return 'الإعداد المسبق: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'تعطيل';
+
   @override
   String get alarmCardVacationPausedBadge => 'متوقفة مؤقتًا بسبب الإجازة';
 }

lib/l10n/gen/app_localizations_bn.dart

@@ -1697,6 +1697,9 @@ class AppLocalizationsBn extends AppLocalizations {
     return 'প্রিসেট: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'বন্ধ করুন';
+
   @override
   String get alarmCardVacationPausedBadge => 'ছুটির কারণে বিরত';
 }

lib/l10n/gen/app_localizations_de.dart

@@ -1710,6 +1710,9 @@ class AppLocalizationsDe extends AppLocalizations {
     return 'Voreinstellung: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Deaktivieren';
+
   @override
   String get alarmCardVacationPausedBadge => 'Wegen Urlaub pausiert';
 }

lib/l10n/gen/app_localizations_en.dart

@@ -1690,6 +1690,9 @@ class AppLocalizationsEn extends AppLocalizations {
     return 'Preset: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Disable';
+
   @override
   String get alarmCardVacationPausedBadge => 'Paused for vacation';
 }

lib/l10n/gen/app_localizations_es.dart

@@ -1704,6 +1704,9 @@ class AppLocalizationsEs extends AppLocalizations {
     return 'Preset: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Desactivar';
+
   @override
   String get alarmCardVacationPausedBadge => 'Pausada por vacaciones';
 }

lib/l10n/gen/app_localizations_fr.dart

@@ -1713,6 +1713,9 @@ class AppLocalizationsFr extends AppLocalizations {
     return 'Préréglage : $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Désactiver';
+
   @override
   String get alarmCardVacationPausedBadge => 'En pause pour les vacances';
 }

lib/l10n/gen/app_localizations_hi.dart

@@ -1692,6 +1692,9 @@ class AppLocalizationsHi extends AppLocalizations {
     return 'प्रीसेट: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'बंद करें';
+
   @override
   String get alarmCardVacationPausedBadge => 'छुट्टी के कारण रोका गया';
 }

lib/l10n/gen/app_localizations_id.dart

@@ -1700,6 +1700,9 @@ class AppLocalizationsId extends AppLocalizations {
     return 'Prasetel: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Nonaktifkan';
+
   @override
   String get alarmCardVacationPausedBadge => 'Dijeda karena liburan';
 }

lib/l10n/gen/app_localizations_it.dart

@@ -1712,6 +1712,9 @@ class AppLocalizationsIt extends AppLocalizations {
     return 'Preset attivo: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Disattiva';
+
   @override
   String get alarmCardVacationPausedBadge => 'In pausa per le vacanze';
 }

lib/l10n/gen/app_localizations_ja.dart

@@ -1643,6 +1643,9 @@ class AppLocalizationsJa extends AppLocalizations {
     return 'プリセット: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => '無効化';
+
   @override
   String get alarmCardVacationPausedBadge => '休暇のため一時停止中';
 }

lib/l10n/gen/app_localizations_pt.dart

@@ -1700,6 +1700,9 @@ class AppLocalizationsPt extends AppLocalizations {
     return 'Predefinição: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Desativar';
+
   @override
   String get alarmCardVacationPausedBadge => 'Pausada por férias';
 }

lib/l10n/gen/app_localizations_ru.dart

@@ -1704,6 +1704,9 @@ class AppLocalizationsRu extends AppLocalizations {
     return 'Пресет: $preset';
   }
 
+  @override
+  String get autoEqDisableOption => 'Отключить';
+
   @override
   String get alarmCardVacationPausedBadge => 'Приостановлено на время отпуска';
 }

lib/l10n/gen/app_localizations_zh.dart

@@ -1635,6 +1635,9 @@ class AppLocalizationsZh extends AppLocalizations {
     return '预设：$preset';
   }
 
+  @override
+  String get autoEqDisableOption => '关闭';
+
   @override
   String get alarmCardVacationPausedBadge => '因假期已暂停';
 }