feat(deploy): 画布 Agent - 独立 yingce-agent 容器并修复运行中断

生产会话不再因 stdout 管道提前关闭被误判失败。设置 YINGCE_AGENT_URL 后只走独立容器，失败不回退到内嵌进程。

backend/agent-runtime/pi/package.json

@@ -8,6 +8,7 @@
   "dependencies": {
     "@earendil-works/pi-ai": "0.87.1",
     "@earendil-works/pi-coding-agent": "0.87.1",
-    "typebox": "1.3.27"
+    "typebox": "1.3.27",
+    "undici": "7.28.0"
   }
 }