fix(upload): 分片用 multipart 字段 chunk、路由顺序与串行上传

- 前端 FormData+chunk，避免 raw body 被中间层断连
- Gin 分片路由置于 POST .../assets 之前
- 分片并发降为 1

Made-with: Cursor

admin/src/api/admin.js

@@ -103,11 +103,14 @@ export const initMultipartUpload = (siteId, body) =>
 export const getMultipartUploadStatus = (siteId, uploadId) =>
   request.get(`/admin/sites/${siteId}/assets/multipart/${uploadId}/status`, { timeout: 60000 })
 
-export const putMultipartChunk = (siteId, uploadId, chunkIndex, blob) =>
-  request.post(`/admin/sites/${siteId}/assets/multipart/${uploadId}/chunk/${chunkIndex}`, blob, {
-    headers: { 'Content-Type': 'application/octet-stream' },
+export const putMultipartChunk = (siteId, uploadId, chunkIndex, blob) => {
+  const fd = new FormData()
+  fd.append('chunk', blob, 'part.bin')
+  // 不传 Content-Type，由浏览器带 boundary；与整文件 multipart 一致，减少中间层断连
+  return request.post(`/admin/sites/${siteId}/assets/multipart/${uploadId}/chunk/${chunkIndex}`, fd, {
     timeout: 180000
   })
+}
 
 export const completeMultipartUpload = (siteId, uploadId) =>
   request.post(`/admin/sites/${siteId}/assets/multipart/${uploadId}/complete`, {}, { timeout: 600000 })

admin/src/utils/siteAssetResumableUpload.js

@@ -9,7 +9,8 @@ import {
 
 const CHUNK_THRESHOLD = 8 * 1024 * 1024
 const DEFAULT_CHUNK_SIZE = 4 * 1024 * 1024
-const UPLOAD_CONCURRENCY = 3
+// 串行上传分片，避免 HTTP/2 多路复用 + 大 body 在部分反代上不稳定
+const UPLOAD_CONCURRENCY = 1
 
 function fileFingerprint(file) {
   return `${file.name}\t${file.size}\t${file.lastModified}`