Clear queue on leave operation

Added a call to `getQueueManager().clearQueue()` in the leave method of `MusicManager`. This ensures the queue is properly cleared when the bot disconnects from a guild, improving consistency and preventing leftover queue data.

src/main/java/me/bobert/netneutrality/music/MusicManager.java

@@ -149,6 +149,7 @@ public class MusicManager implements MusicManagerCallback {
             guild.getJDA().getDirectAudioController().disconnect(guild);
         }
 
+        getQueueManager().clearQueue();
         scheduler.detachContext();
     }