fix: 'best' format on audio-only sites (SoundCloud) now shows audio containers

- When content is audio-only (IsAudioOnlyContent), 'best' format is marked as
  IsAudioOnly so determineMediaType returns MediaTypeAudio
- Previously 'best' was hardcoded with HasVideo:true, causing video containers
  (mp4/mkv) to be shown instead of audio containers (mp3/m4a/opus)

internal/handler/download.go

@@ -166,7 +166,11 @@ func (h *Handler) handleFormatSelection(ctx context.Context, chatID int64, msgID
 	ss.MainFormatID = formatID
 
 	if formatID == "best" {
+		if ss.MediaInfo.IsAudioOnlyContent() {
+			ss.MainFormat = &domain.Format{ID: "best", HasAudio: true, IsAudioOnly: true}
+		} else {
 			ss.MainFormat = &domain.Format{ID: "best", HasVideo: true, HasAudio: true}
+		}
 		h.advanceToLanguage(ctx, chatID, msgID, userID, ss)
 		return
 	}