refactor(comment): 移除评论回复中的用户名前缀

移除了在 PlaylistDetail 和 SingerDetail 组件中设置回复对象时，自动添加的用户名前缀。这个改动简化了回复流程，用户现在需要手动输入回复内容。

music-qianduan/src/views/PlaylistDetail.vue

@@ -190,7 +190,6 @@ const toggleReplies = (comment) => {
 const setReplyTo = (comment) => {
   replyingTo.value = comment.id;
   replyTo.value = comment;
-  replyContent.value = `@${comment.user.username} `;
   if (!expandedComments.value.includes(comment.id)) {
     expandedComments.value.push(comment.id);
   }

music-qianduan/src/views/SingerDetail.vue

@@ -209,7 +209,6 @@ const toggleReplies = (comment) => {
 const setReplyTo = (comment) => {
   replyingTo.value = comment.id;
   replyTo.value = comment;
-  replyContent.value = `@${comment.user.username} `;
   if (!expandedComments.value.includes(comment.id)) {
     expandedComments.value.push(comment.id);
   }