CVE-2026-72713: fallo de gravedad alta en OpenBMB XAgent

XAgent contains a path traversal vulnerability in the workspace file endpoint that allows self-registered or default-credential users to read arbitrary files on the host by supplying parent-directory segments in the `file_name` form field with no path containment check. Attackers can register an account without email verification, then submit crafted `file_name` values such as parent-directory traversal sequences to the `/workspace/file` handler to read host files including application secrets, database credentials, and system files outside the Docker sandbox.