feat(eq): android auto custom equalizer and robust device detection

- MainActivity: onListen re-emits the current active device and registers
  the audio device callback idempotently, so recreated activities resync
  instead of freezing the active-device id on a disconnected device.
- servicio_dispositivo_audio: resubscribir() re-opens the event channel;
  estado_ecualizador exposes refrescarDispositivoActual() with an
  in-flight guard, invoked on app resume and when opening advanced EQ
  options, clearing stale green-dot device selections.
- navegacion_auto/servicio_audio: new 'Personalizado' browse tree in
  Android Auto (5 band folders, 13 gain steps each) applied live via
  setBanda; preset and gain taps persist at device level when
  multi-device EQ is active and respect station/matrix overrides,
  with apply-before-persist ordering and children-changed notifications.
- l10n: regenerate stale generated localizations; add rxdart as direct
  dependency for the subscribeToChildren override.

lib/l10n/gen/app_localizations_zh.dart

@@ -62,22 +62,22 @@ class AppLocalizationsZh extends AppLocalizations {
     Object minutes,
     Object seconds,
   ) {
-    return '$hours ?? $minutes ? $seconds ?';
+    return '$hours小时$minutes分钟$seconds秒';
   }
 
   @override
   String durationMinutesSeconds(Object minutes, Object seconds) {
-    return '$minutes ? $seconds ?';
+    return '$minutes分钟$seconds秒';
   }
 
   @override
   String durationMinutesOnly(Object minutes) {
-    return '$minutes ?';
+    return '$minutes分钟';
   }
 
   @override
   String durationSecondsOnly(Object seconds) {
-    return '$seconds ?';
+    return '$seconds秒';
   }
 
   @override
@@ -1256,4 +1256,33 @@ class AppLocalizationsZh extends AppLocalizations {
 
   @override
   String get eqDeviceConnected => '已连接';
+
+  @override
+  String get localMusicSectionTitle => '本地音乐（Android Auto）';
+
+  @override
+  String get localMusicSectionDescription => '选择此设备上的一个文件夹，以便在车内浏览和播放其中的音频文件。';
+
+  @override
+  String get localMusicFolderNotConfigured => '未选择文件夹';
+
+  @override
+  String get localMusicFolderTitle => '本地音乐文件夹';
+
+  @override
+  String get localMusicChoosePath => '选择文件夹';
+
+  @override
+  String get localMusicChangePath => '更改文件夹';
+
+  @override
+  String get localMusicFolderUpdated => '本地音乐文件夹已更新';
+
+  @override
+  String localMusicFolderSaveError(Object error) {
+    return '无法保存文件夹：$error';
+  }
+
+  @override
+  String get localMusicFolderGenericName => '已选文件夹';
 }