feat(piadmin): 支持多文件上传功能

- 新增多文件上传处理逻辑
- 遍历上传文件数组并逐个处理
- 返回所有上传文件的结果集合
- 兼容单文件和多文件上传场景

plugin/piadmin/app/controller/v1/AttachmentController.php

@@ -26,6 +26,13 @@ class AttachmentController extends BaseController
     public function upload()
     {
         $file = request()->file('file');
+        if (is_array($file)) {
+            $oss_files = [];
+            foreach ($file as $item) {
+                $oss_files[] = $this->service->upload($item);
+            }
+            return success($oss_files);
+        }
         return success($this->service->upload($file));
     }