fix(player): backtick doc-comment generics (analyze --fatal-infos)

`Future<dynamic>` in the customAction doc comment tripped
unintended_html_in_doc_comment (bare angle brackets read as HTML).
Wrap the code identifiers in backticks.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/lib/player/audio_handler.dart

@@ -670,7 +670,7 @@ class MinstrelAudioHandler extends BaseAudioHandler with QueueHandler, SeekHandl
   /// Handles the notification favorite control (and any future custom
   /// actions). Toggles the current track's like via the LikeBridge,
   /// then re-broadcasts so the heart icon/label flips. Signature
-  /// matches AudioHandler.customAction (Future<dynamic>).
+  /// matches `AudioHandler.customAction` (`Future<dynamic>`).
   @override
   Future<dynamic> customAction(String name,
       [Map<String, dynamic>? extras]) async {