feat(player): language-first audio & subtitle track labels

close #1307

lib/utils/codec_utils.dart

@@ -72,6 +72,23 @@ class CodecUtils {
     };
   }
 
+  /// Formats an audio channel count as a friendly layout name (2 → 'Stereo',
+  /// 6 → '5.1'). Returns null when [channels] is null or not positive.
+  static String? formatAudioChannels(int? channels) {
+    if (channels == null || channels <= 0) return null;
+    return switch (channels) {
+      1 => 'Mono',
+      2 => 'Stereo',
+      3 => '3.0',
+      4 => '4.0',
+      5 => '4.1',
+      6 => '5.1',
+      7 => '6.1',
+      8 => '7.1',
+      _ => '${channels}ch',
+    };
+  }
+
   /// Formats an audio codec name to a user-friendly display format.
   static String formatAudioCodec(String codec) {
     final lower = codec.toLowerCase();