Skip webhook server on EADDRINUSE, bump to 0.9.7

[pallaoro]

Summary

• Plugin loads run in both the OpenClaw gateway daemon and the CLI; both call register(), both attempted to bind the webhook port, second one crashed with EADDRINUSE.
• startWebhookServer now installs a server.on("error") handler that logs a warning and no-ops on EADDRINUSE, letting whichever instance binds first own the port.
• Other listen errors still surface as errors.

Test plan

• npm run lint clean
• npm test — 117/117 pass
• Manual: run two clawflow-loading processes against the same port; second should warn and continue rather than crash