fix: null-guard queueRepository in GuildMusicManager — radio passes null, was NPE'ing in constructor

RadioManager creates GuildMusicManager with null queueRepository (radio has no
queue persistence). Constructor called loadQueueAsync() which dereferenced null,
throwing NPE after voice connect — bot joined voice but track never loaded.

src/main/java/creator/loki/feature/music/manage/GuildMusicManager.java

@@ -100,6 +100,7 @@ public class GuildMusicManager {
   }
 
   private void loadQueueAsync() {
+    if (queueRepository == null) return;
     var saved = queueRepository.loadQueue(String.valueOf(guildId));
     if (saved.isEmpty()) return;
     var client = lavalinkManager.getClient();
@@ -136,6 +137,7 @@ public class GuildMusicManager {
   }
 
   void saveQueue() {
+    if (queueRepository == null) return;
     var current = scheduler.getCurrentTrack();
     var tracks = new ArrayList<>(scheduler.getQueue());
     var queueTracks = new ArrayList<QueueTrack>();