feat(P3): 私信 + #话题标签 + @提及 完成

backend/internal/video/video_service.go

@@ -60,8 +60,14 @@ func (vs *VideoService) Publish(ctx context.Context, video *Video) error {
 		if err := tx.Create(&msg).Error; err != nil {
 			return err
 		}
-		return nil
 
+		tags := ExtractTags(video.Title + " " + video.Description)
+		for _, tagName := range tags {
+			var tag Tag
+			tx.Where("name = ?", tagName).FirstOrCreate(&tag, Tag{Name: tagName})
+			tx.Create(&VideoTag{VideoID: video.ID, TagID: tag.ID})
+		}
+		return nil
 	})
 	return err