Co-author trailers are dropped from a freshly-created release PR (create path doesn't thread co-authors) #301

Problem

The Co-authored-by trailer block added in #292 (so GitHub credits contributors on the squashed release commit) is threaded into the release-PR refresh path but not the create path. A release PR opened by create-release-pr therefore has no trailer until some later push to next/hotfixes triggers a refresh. If a release is created and merged before any refresh, the squash commit ships with contributors uncredited — the exact case #292 set out to fix.

Where

Both release-PR actions run generate-comprehensive-changelog, which produces a co-authors output:

• actions/github/jobs/update-release-pr (refresh) routes the body through update-pr-changelog and threads it: co-authors: ${{ steps.changelog.outputs.co-authors }} (action.yml:249). ✅
• actions/github/jobs/create-release-pr (initial create) writes the body via actions/github/api/pull-requests with body-content: ${{ steps.changelog.outputs.changelog-content }} (action.yml:284) and never references the co-authors output. The pull-requests action takes a single body-content and writes it verbatim — no co-authors handling. ❌

Evidence

CLDMV/.github #300 (release: v4.27.5) was opened by create-release-pr and its body has the 👥 Contributors details but no <!-- co-authors --> / Co-authored-by: block.

Proposed fix

Give the create path the same dead-last append the refresh path gets:

1. actions/github/api/pull-requests/action.mjs — add an optional co-authors input; when non-empty, append it as the final paragraph before create/update: bodyContent = bodyContent.replace(/\s+$/, "") + "\n\n" + coAuthors (the same rule update-pr-changelog uses, so a later update-pr-coverage insert still lands above the <!-- co-authors --> marker and the trailers stay last).
2. actions/github/api/pull-requests/action.yml — declare the co-authors input.
3. actions/github/jobs/create-release-pr/action.yml — pass co-authors: ${{ steps.changelog.outputs.co-authors }} to that step.

Scope

Affects every CLDMV repo on the v4 release flow — any release PR is uncredited from creation until its first refresh. Follow-up to #292.