docs: attribution footer for machine-opened issues and PRs

Mirror of dank/command-center's rule (there: PR off docs/session-trailer-rule).
Every agent-opened issue/PR body ends with cwd + omp session id so machine-filed
artifacts trace back to the box and session that produced them.

Refs #11 (command-center tracker)

AGENTS.md

@@ -71,6 +71,15 @@ the same regime.
 7. **Pull** on the target (`deploy.sh` does this)
 8. **Deploy** — `scripts/deploy.sh` plans and dispatches only changed services
 
+**Attribution footer (issues and PRs)** — every issue or PR body you open MUST end with:
+
+```
+---
+cwd: <working directory> · session: <omp session id>
+```
+
+Session id from `/status`. Machine-made artifacts stay attributable to the box and session that spawned them.
+
 ## Deployment
 
 ```