fix: 评论系统全量检查修复（7 项 Gap 全部修复）

- Delete 权限：新增 requesterID/isAdmin 参数，Service 层鉴权（仅本人/管理员可删）
- 通知内容：改用 GetUsernameByID 显示真实用户名，非数字 UID
- SearchUsers：Repository 返回 exp，Service 调用 GetLevelByExp 计算等级
- 通知高亮：Notification 新增 CommentID 字段，消息链接支持 #comment-{id}
- 已删除提示：前端 hash 检测 + 3 秒超时 Toast "该评论已不存在"
- Admin CSS：移除不存在的 comments.css 引用
- 错误哨兵：改用 common.ErrCommentNotFound/ErrCommentEmpty/PermissionDenied

internal/service/notification_service.go

@@ -26,7 +26,7 @@ func NewNotificationService(repo notifRepo) *NotificationService {
 }
 
 // Create 创建消息
-func (s *NotificationService) Create(userID uint, notifyType, title, content string, relatedID *uint) error {
+func (s *NotificationService) Create(userID uint, notifyType, title, content string, relatedID, commentID *uint) error {
 	n := &model.Notification{
 		UserID:     userID,
 		NotifyType: notifyType,
@@ -34,6 +34,7 @@ func (s *NotificationService) Create(userID uint, notifyType, title, content str
 		Content:    content,
 		IsRead:     false,
 		RelatedID:  relatedID,
+		CommentID:  commentID,
 	}
 	return s.repo.Create(n)
 }
@@ -92,7 +93,7 @@ func (s *NotificationService) NotifyAuditApproved(userID uint, auditType string,
 	_ = s.Create(userID, model.NotifyAuditApproved,
 		"审核已通过",
 		"你的"+typeName+"修改已通过审核",
-		&relatedID)
+		&relatedID, nil)
 }
 
 // NotifyAuditRejected 审核拒绝通知
@@ -108,14 +109,14 @@ func (s *NotificationService) NotifyAuditRejected(userID uint, auditType, reason
 	_ = s.Create(userID, model.NotifyAuditRejected,
 		"审核未通过",
 		content,
-		&relatedID)
+		&relatedID, nil)
 }
 
 // NotifyPostApproved 稿件审核通过通知
 func (s *NotificationService) NotifyPostApproved(userID uint, postTitle string, postID uint) {
 	title := "稿件审核通过"
 	content := "你的稿件《" + postTitle + "》已通过审核，现已公开发布"
-	_ = s.Create(userID, model.NotifyPostApproved, title, content, &postID)
+	_ = s.Create(userID, model.NotifyPostApproved, title, content, &postID, nil)
 }
 
 // NotifyPostRejected 稿件审核拒绝通知
@@ -125,5 +126,5 @@ func (s *NotificationService) NotifyPostRejected(userID uint, postTitle, reason
 	if reason != "" {
 		content += "，理由：" + reason
 	}
-	_ = s.Create(userID, model.NotifyPostRejected, title, content, &postID)
+	_ = s.Create(userID, model.NotifyPostRejected, title, content, &postID, nil)
 }