refactor(annotation): 简化注释数据导出下载逻辑

- 移除前端手动创建 a 标签下载文件的方式
- 将文件名参数传递给后端 API 函数
- 利用 download 函数内置的下载处理机制
- 简化 ExportAnnotationDialog 组件中的导出流程
- 更新 annotation.api.ts 中的 downloadAnnotationsUsingGet 函数签名
- 直接通过 API 调用完成文件下载和命名

frontend/src/pages/DataAnnotation/annotation.api.ts

@@ -109,12 +109,13 @@ export function downloadAnnotationsUsingGet(
   projectId: string,
   format: ExportFormat = "json",
   onlyAnnotated: boolean = true,
-  includeData: boolean = false
+  includeData: boolean = false,
+  filename?: string
 ) {
   const params = new URLSearchParams({
     format,
     only_annotated: String(onlyAnnotated),
     include_data: String(includeData),
   });
-  return download(`/api/annotation/export/projects/${projectId}/download?${params.toString()}`);
+  return download(`/api/annotation/export/projects/${projectId}/download?${params.toString()}`, null, filename);
 }