rubygems-release: guarantee GitHub Release for every published tag (closes ci#354)

[opoudjis]

Closes #354

Summary

Two coordinated changes: (1) the release-notes floor on rubygems-release.yml, and (2) the opt-out variants for the 27 opoudjis-maintained gems that write their notes by hand.

Part 1 — release-notes floor in rubygems-release.yml

Adds a mechanical floor: every tag pushed by the shared workflow carries a GitHub Release with at least auto-generated notes (PR titles since the previous tag). Closes the class where a gem accumulates tags with no releases (metanorma-plugin-lutaml v0.7.35-v0.7.50 hit this before backfill; the same pattern recurs elsewhere in the stack).

New input

release_notes: 'auto' (default) | 'manual'

• auto — if no Release exists for the pushed tag, create one with auto-generated notes (PR titles since the previous tag).
• manual — skip the ensure-release step entirely.

Never overwrite

If a Release already exists for the tag (whether from a hand-written maintainer note or a prior workflow run), the step detects it via gh release view and leaves it alone. gh release create only fires on the not-exists path.

Placement

The new step lives at the end of the release job, right after the "Verify gem published on rubygems.org" post-publish check and before the "Post-release event" repository_dispatch. Runs on the same SHOULD_PUBLISH / skip_push gates as the publish step itself, plus release_notes != 'manual'.

Auth

Uses the release job's existing contents: write permission (inherited from the caller — every current caller template carries contents: write per ci#339). No new secret required.

Part 2 — opt-out variants for 27 opoudjis-maintained gems

Per opoudjis's decision on the ticket, the floor is opt-out for gems whose maintainers write release notes by hand at release time. Introduces two variant caller templates + updates 27 cimas.yml mappings.

Variant templates (2 new files)

• cimas-config/gh-actions/master/release_manual_notes.yml — variant of release.yml that passes release_notes: manual to the reusable.
• cimas-config/gh-actions/master/release_wo_bundle_install_manual_notes.yml — variant of release_wo_bundle_install.yml with the same opt-out.

Each variant file carries a header block naming its parent template, its consumer set, and how to switch back to the auto-notes floor. Same per-variant documentation discipline established with Gemfile.grammar-build in ci#353.

cimas.yml mapping updates (27)

• 24 gems switching from release.yml → release_manual_notes.yml:
  metanorma-cli, metanorma-core, metanorma-ogc, metanorma-cc, metanorma-ribose, metanorma-iho, metanorma-ieee, metanorma-iec, metanorma-ietf, metanorma-standoc, metanorma-iso, metanorma-taste, metanorma-itu, metanorma-generic, metanorma-bipm, metanorma-jis, metanorma-plateau, metanorma-document, isodoc, isodoc-i18n, html2doc, gb-agencies, cnccs, isoics.
• 3 gems switching from release_wo_bundle_install.yml → release_wo_bundle_install_manual_notes.yml:
  metanorma-utils, metanorma (top-level), mn-requirements.

Exempt-by-construction (no variant needed)

• metanorma-nist and metanorma-bsi map release_github_packages.yml, which calls ghpkg-release.yml, not rubygems-release.yml. Part 1's floor lives in rubygems-release.yml and doesn't reach the ghpkg-release path. Those two gems are already exempt without any variant mapping.

Non-opoudjis gems

Every gem not in the opt-out list keeps its current mapping and gets the auto-notes floor on their next release run. This is the intended default per ticket #354.

Effect after next cimas wave (~2026-07-22)

• Non-opt-out gems: their next release carries auto-generated Release notes if none exist, hand-written notes preserved if they do.
• Opt-out gems (the 27 above): their release.yml gets synced to the variant, workflow skips the ensure-release step, maintainer authors Release + notes by hand.

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