fix: create the update directory for fresh named volumes [CI]

ConfigStore.Write only created the config root, so a new volume without update/ made update offers fail with IO_PathNotFound. Create the parent directory on write and ship an empty update/ in the node images.

ci/stage-node-image.py

@@ -59,6 +59,9 @@ def stage(component: str, destination: Path) -> None:
     config = destination / "config"
     config.mkdir()
     (config / ".keep").write_text("", encoding="utf-8")
+    # 更新清单和请求放在这里；空的命名卷第一次挂载时会带上这个目录
+    (config / "update").mkdir()
+    (config / "update" / ".keep").write_text("", encoding="utf-8")
 
 
 def main() -> None: