fix: proxy embed to A public host with correct Host/SNI [deploy]

Dockerfile

@@ -1,7 +1,7 @@
 # CI 中先 pnpm build 产出 dist/；运行时由 nginx 托管，并把 /embed /images /api/contact 反代到 A 站
 FROM nginx:1.27-alpine
 
-ENV A_UPSTREAM=http://project57-deploy.ns-project57.svc.cluster.local:3000
+ENV A_UPSTREAM=https://project57.website-build.org
 
 # 不走 templates/envsubst，避免把 nginx 的 $host/$uri 清空
 COPY nginx.conf /etc/nginx/conf.d/default.conf