feat: @提及发送通知 + 通知点击定位高亮

- 新增 NotifyCommentMention 通知类型，归属 mention 分类 TAB
- parseMentions 中向被@用户发送通知（排除自己和重复通知）
- 消息中心 mention 通知可点击跳转至文章页面
- 通过 mention 通知进入时，来源评论置顶并持久半透明高亮
- 普通评论链接保持原有短暂高亮行为不变

internal/model/notification.go

@@ -11,8 +11,9 @@ const (
 	NotifyLevelUp         = "level_up"
 	NotifyComment         = "comment"
 	NotifyCommentReply    = "comment_reply"
-	NotifyLikeAggregated  = "like_aggregated" // 每日聚合点赞通知
-	NotifyFollow          = "follow"           // 关注通知
+	NotifyLikeAggregated  = "like_aggregated"  // 每日聚合点赞通知
+	NotifyFollow          = "follow"            // 关注通知
+	NotifyCommentMention  = "comment_mention"   // 评论@提及通知
 )
 
 // Notification 消息/通知模型
@@ -39,6 +40,7 @@ var NotifyTypeNames = map[string]string{
 	NotifyLevelUp:        "等级提升",
 	NotifyComment:        "评论",
 	NotifyCommentReply:   "回复",
+	NotifyCommentMention: "@ 提及",
 	NotifyLikeAggregated: "点赞",
 	NotifyFollow:         "关注",
 }
@@ -54,6 +56,7 @@ var NotifyCategory = map[string]string{
 	NotifyLevelUp:        "system",
 	NotifyComment:        "mention",
 	NotifyCommentReply:   "mention",
+	NotifyCommentMention: "mention",
 	NotifyLikeAggregated: "like",
 	NotifyFollow:         "follow",
 }