Closes#9. .github/workflows/release.yml (workflow_call) replaces box's,
rig's and cast's release.yml: the merge door (facts -> decide -> notes ->
tag+publish+bump, every decision in a tested lib script) and the tag door
(the manual fallback and backfill, no bump). Plus lib/facts.sh (the merge
door's impure half, contract-tested against fixture repos with a stubbed
gh), the self-ref pin guard (.github/scripts/self-ref-check.sh + CI step +
tests), the release-exercise scratch caller (dry wiring), the end-to-end
script-chain rehearsal, and the caller + artifact-hook contracts in
docs/CONSUMERS.md.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
