"[Unreleased] is not a terminal state" — add release-cutting triggers to the standard

[PBNZ]

Retrospective finding — refs #10.

Context

Across the retrospective sample, changelog writing is in good shape — but four of eight repos
ended with their entire history sitting in ## [Unreleased] despite shipped artifacts, a
built-but-never-triggered tag pipeline, or versioned outputs already in use elsewhere. Where
releases were cut, the changelogs are exemplary. The failure is never the writing — it's that
the standard defines how to keep [Unreleased], but names no moment at which to cut it, so solo
projects simply never do.

Side effect observed: a years'-worth [Unreleased] block accretes append-position churn (entries
pasted out of order) and stops being readable as "what's new".

Proposal

Add a short "when to cut a release" section to the commit/changelog conventions:

1. Cut triggers — cut a version the first time any of these happens: an artifact is handed to
   anyone else (deployed, published, installed on a second machine), a version number is stamped
   into any output, or a tag pipeline exists and has never fired.
2. Checklist line in the pre-PR/pre-commit checklist: "does [Unreleased] describe more than
   one shippable unit? If yes, cut."
3. Documented lightweight variant for genuinely never-versioned repos (internal ops repos):
   dated changelog entries instead of versions — one repo in the sample already does this well;
   make it an official, declared variant instead of an ad-hoc deviation.
4. Optional CI nudge: warn when [Unreleased] exceeds N entries while release machinery
   exists in the repo.

Tasks

• Extend the commit-conventions reference with the cut triggers + the dated-entries variant.
• Add the checklist line.
• Provide the CI nudge snippet (opt-in).

Acceptance criteria

• The standard answers "when do I cut?" in one place, with the no-version variant defined.
• A repo with a tag pipeline and a fat [Unreleased] gets flagged by checklist or CI, not by
  archaeology.

— 🤖 Claude, on behalf of @PBNZ

[PBNZ]

Triage: accepted (adapted: the CI nudge is a documented opt-in snippet).

Landed on PR #18 (commit f3875c8): commit-conventions.md gains When to cut a release — cut the first time an artifact leaves the repo, a version is stamped into any output, or a tag pipeline exists and has never fired. Pre-PR tripwire: "does [Unreleased] describe more than one shippable unit? If yes, cut." The never-versioned dated-entries variant is now an official declared variant (START-HERE row), and the [Unreleased]-entry-count warning ships as a copy-paste snippet.

— 🤖 Claude, on behalf of @PBNZ

[PBNZ]

Verified on main (f7ab31c): When to cut a release in commit-conventions.md (triggers, dated-entries variant, CI nudge) + pre-PR tripwire. Fittingly, the trigger has already fired for this repo — 0.4.0 is due. Closing on @PBNZ's instruction.

— 🤖 Claude, on behalf of @PBNZ