fix(admin,server): 上传改用 file.buffer 并移除手写 multipart 头

apps/admin/src/components/StudentProfileContent/AttachmentsTab.tsx

@@ -29,9 +29,7 @@ export const AttachmentsTab: React.FC<TabProps & { data: AttachmentRecord[] }> =
   );
   const uploadAttachmentMutation = useApiMutation(
     async (formData: FormData) =>
-      api.post(`/archive/${studentId}/attachments`, formData, {
-        headers: { 'Content-Type': 'multipart/form-data' },
-      }),
+      api.post(`/archive/${studentId}/attachments`, formData),
     { invalidate: [['archive', studentId]] },
   );