Enforce defense-in-depth in release workflows

When modifying GitHub Actions release, approval, or CI-poller flows, preserve strict trust boundaries and fail closed. Run only trusted default-branch code before accessing tokens, keep secret-bearing jobs behind the protected production environment, prevent dispatched refs from receiving secrets, and pin actions and containers to immutable digests. Bind approvals to immutable request details and current label-event IDs, prohibit self-approval, and revalidate attestations immediately before every privileged state transition or publish operation. If the request or approval changes, remove approval-related labels and stop rather than continuing. Add focused automated tests that enforce workflow ordering, token identity, action pinning, dispatch restrictions, exact body preservation, cleanup, and race-condition handling.