Add CRAN submission workflow triggered on release

[ChrisRackauckas]

Summary

Adds .github/workflows/cran-release.yml that, on a published GitHub release:

1. Builds the source tarball with R CMD build
2. Runs R CMD check --as-cran
3. Attaches the tarball to the GitHub release as an asset
4. Calls devtools::submit_cran() to POST the tarball to CRAN

CRAN then emails the maintainer (from DESCRIPTION) a confirmation link. Clicking that link finalizes the submission — the workflow can't do this for you (and CRAN policy wouldn't want it to).

Manual workflow_dispatch trigger is also available for ad-hoc submissions without cutting a new release.

Required one-time setup before this works

Create a GitHub Environment named cran-submission with required reviewers (yourself):

• Repo Settings → Environments → New environment → name cran-submission
• Configure "Required reviewers" → add your GitHub user
• Save

Why this matters: without the reviewer gate, every published release auto-submits to CRAN. CRAN rejects duplicate submissions of the same version, and accidental re-tags would burn submission slots. The environment gate pauses the workflow at the submission step until you click "Approve" in the Actions UI.

Notes

• Pre-releases are skipped (!github.event.release.prerelease).
• cran-comments.md already exists in the repo — devtools::submit_cran() will use it.
• The CRAN-SUBMISSION file written by devtools is logged in the run output. If you want it committed back to the repo automatically, that's a follow-up — for now you can copy it from the run log.
• TinyTeX is installed so the PDF manual builds during R CMD check.

Test plan

• Create cran-submission environment with required reviewers
• Trigger via workflow_dispatch once to validate build + check pass (cancel before approving the submit step, or let it submit if you're ready)
• Next real release: cut tag v2.1.0, approve the pending workflow run, click the CRAN confirmation email

🤖 Generated with Claude Code