feat(playlist): 增加歌单收藏和评论功能

- 在 CommentServiceImpl 中添加歌单评论相关逻辑
- 在 PlaylistServiceImpl 中实现歌单收藏和取消收藏功能
- 在 PlaylistDetail.vue 中显示歌单的收藏数和评论数
- 更新数据库模型，在 Singer 实体中添加收藏数和评论数字段

music-qianduan/src/views/PlaylistDetail.vue

@@ -141,6 +141,12 @@ const toggleCollect = async () => {
     const res = await toggleCollectPlaylist(playlistId.value)
     if (res.code === 200) {
       isCollected.value = !isCollected.value
+      // 更新收藏数
+      if (isCollected.value) {
+        playlist.value.collectCount++
+      } else {
+        playlist.value.collectCount--
+      }
       ElMessage.success(isCollected.value ? '收藏成功' : '已取消收藏')
     } else {
       ElMessage.error(res.message || '操作失败')
@@ -163,6 +169,8 @@ const deleteComment = async (commentId) => {
     const res = await apiDeleteComment(commentId)
     if (res.code === 200) {
       comments.value = comments.value.filter(c => c.id !== commentId)
+      // 更新评论数
+      playlist.value.commentCount--
       ElMessage.success('评论已删除')
     } else {
       ElMessage.error(res.message || '删除失败')
@@ -256,6 +264,8 @@ const submitComment = async (isReply = false) => {
         commentContent.value = ''
       }
       ElMessage.success('评论已发送')
+      // 更新评论数
+      playlist.value.commentCount++
     } else {
       ElMessage.error(res.message || '评论失败')
     }
@@ -388,6 +398,11 @@ onUnmounted(() => {
           </div>
           <div class="playlist-time">创建时间：{{ playlist.createTime }}</div>
           <div class="playlist-count">播放次数：{{ formatPlayCount(playlist.playCount) }}</div>
+          <div class="playlist-stats">
+            <span>收藏数：{{ playlist.collectCount }}</span>
+            <el-divider direction="vertical" />
+            <span>评论数：{{ playlist.commentCount }}</span>
+          </div>
           <div class="playlist-desc">{{ playlist.description }}</div>
 
           <div class="playlist-actions">
@@ -488,7 +503,7 @@ onUnmounted(() => {
           ></el-empty>
         </el-tab-pane>
 
-        <el-tab-pane label="评论">
+        <el-tab-pane :label="`评论(${playlist.commentCount || 0})`">
           <!-- 评论输入框 -->
           <div class="comment-input">
             <el-input