Require release documentation sweep

[Maples7]

Summary

• add an AGENTS.md rule requiring every release PR to check the official Agent runbook, README family, command reference, cookbook, and other user-facing docs
• require stale user-facing docs to be updated in the release PR, or for the PR body to state docs were reviewed and no changes were needed

Notes

• Follow-up to v0.9.0: the release PR had already merged and the tag had already been pushed before this rule was requested.

Tests

• Not run; docs-only AGENTS.md update.