feat: @搜索优先展示已关注用户，结果限制最多5条

- SearchUsersByLevel SQL新增LEFT JOIN user_follows，按已关注优先+exp降序
- SearchUsers/followerUID参数贯穿repo→service→controller
- 继续输入时前端自动重新搜索新关键词

internal/service/comment_service.go

@@ -190,9 +190,9 @@ func (s *CommentService) ListAllComments(keyword string, showDeleted bool, page,
 	return rows, total, err
 }
 
-// SearchUsers 搜索LV2+用户（用于@艾特悬浮窗）
-func (s *CommentService) SearchUsers(keyword string) ([]model.UserSearchResult, error) {
-	rows, err := s.repo.SearchUsersByLevel(keyword, 2, 10)
+// SearchUsers 搜索LV2+用户（用于@艾特悬浮窗），已关注优先，最多5条
+func (s *CommentService) SearchUsers(keyword string, followerUID uint) ([]model.UserSearchResult, error) {
+	rows, err := s.repo.SearchUsersByLevel(keyword, 2, 5, followerUID)
 	if err != nil {
 		return nil, fmt.Errorf("搜索用户失败: %w", err)
 	}
@@ -219,7 +219,7 @@ func (s *CommentService) parseMentions(commentID uint, body string) {
 			continue
 		}
 		seen[username] = true
-		rows, _ := s.repo.SearchUsersByLevel(username, 2, 1)
+		rows, _ := s.repo.SearchUsersByLevel(username, 2, 1, 0)
 		if len(rows) > 0 {
 			_ = s.repo.CreateMention(&model.CommentMention{
 				CommentID:        commentID,

internal/service/repository.go

@@ -155,7 +155,7 @@ type commentStore interface {
 	CreateMention(mention *model.CommentMention) error
 	FindPostIDByComment(commentID uint) (uint, error)
 	FindPostAuthorID(postID uint) (uint, error)
-	SearchUsersByLevel(keyword string, minLevel, limit int) ([]struct {
+	SearchUsersByLevel(keyword string, minLevel, limit int, followerUID uint) ([]struct {
 		UID      uint
 		Username string
 		Avatar   string