ci: validate no-mistakes PR signature contract

[ruby-dlee]

Intent

Preserve the stranded CI baseline fixes on PR 60, refresh them onto current main, and get the existing PR genuinely green without running the live-fleet local test suite.

What Changed

• Add a regression test that keeps the required no-mistakes PR marker synchronized between the GitHub workflow and contributor documentation.
• Document the exact machine-verifiable marker required in generated PR pipeline sections.
• Remove the overridden metadata-lock wait timeout from the abandoned-reclaimer test fixture.

Risk Assessment

✅ Low: The change is narrowly scoped to stabilizing an existing lock-reclamation test and synchronizing the documented no-mistakes PR marker with its CI contract, with no material source risk identified.

Testing

• ⏭️ Test - skipped

Pipeline

Updates from git push no-mistakes

✅ **intent** - passed

✅ No issues found.

✅ **Rebase** - passed

✅ No issues found.

✅ **Review** - passed

✅ No issues found.

⏭️ **Test** - skipped

Step was skipped.

✅ **Document** - passed

✅ No issues found.

✅ **Lint** - passed

✅ No issues found.

✅ **Push** - passed

✅ No issues found.

[ruby-dlee]

Closing this accidental no-mistakes alias PR; the intended work remains on PR #60, whose current head is being verified.