新增文章模块封面图片功能，包括在数据传输对象、模型和服务中添加封面图片字段，并在推荐服务中更新文章卡片以显示封面图片。

src/articles/articles.service.ts

@@ -18,6 +18,7 @@ export class ArticlesService {
       title: dto.title,
       publishedDate: dto.publishedDate as any,
       htmlContent: dto.htmlContent,
+      coverImage: dto.coverImage,
     });
     return { code: ResponseCode.SUCCESS, message: 'success', data: article.toJSON() as ArticleVo };
   }