Plugin idea: webhooks — change-notification webhooks (poll-based) #7

A plugin that POSTs a notification to operator-registered URLs when pod resources change. Because there is no api.events.onResourceChange seam yet (see REPORT.md), it must poll (container-walk on an interval) — which makes it a real integration primitive and another consumer strengthening the events-seam case.

Careful: it makes outbound POSTs to arbitrary operator-supplied URLs, so it needs corsproxy/-grade SSRF gates (reuse the private-IP guard now in activitypub/'s gatedFetch or corsproxy/). That's why it was deferred from the safe waves — build it in a focused session with the gate in place.

Copy from: notifications/ (fs.watch), rss//sparql/ (container walk), corsproxy/ (SSRF gate). See AGENT.md.