docs: 完善AdminApi控制器注释和代码规范

src/Api/TakeoutSaaS.AdminApi/Controllers/FilesController.cs

@@ -20,6 +20,7 @@ public sealed class FilesController(IFileStorageService fileStorageService) : Ba
     /// <summary>
     /// 上传图片或文件。
     /// </summary>
+    /// <returns>文件上传响应信息。</returns>
     [HttpPost("upload")]
     [RequestFormLimits(MultipartBodyLengthLimit = 30 * 1024 * 1024)]
     [ProducesResponseType(typeof(ApiResponse<FileUploadResponse>), StatusCodes.Status200OK)]