Add GitHub release tagging and backfill workflows

[rasmusbe]

Summary

• Add Release workflow: creates an annotated git tag and GitHub Release when setup.py version bumps on version-2 (also supports manual dispatch).
• Add Backfill Releases workflow: one-time restoration of missing tags for releases already published on PyPI.
• No PyPI publishing changes — tags and GitHub Releases only.

Tag format matches PyPI: 2.7.1 (no v prefix). Release notes are taken from the matching line in README Version History when available.

Forward releases (after merge)

1. Bump version= in setup.py and add a line to README Version History.
2. Merge to version-2.
3. The Release workflow runs automatically and creates the tag + GitHub Release.

Manual cut (optional): Actions → Release → Run workflow → set ref if not releasing from version-2.

How to backfill old releases

PyPI has releases back to 2.6.2, but this repo has no git tags. Run backfill once after merging this PR.

Step 1 — Dry run (default)

1. Go to Actions → Backfill Releases → Run workflow.
2. Leave defaults:
   • since: 2.6.2
   • dry_run: true
3. Run and open the backfill-plan artifact (or read the job log).

The table shows each version, matched commit, fingerprint score, and planned action. Rows with skip-low-confidence or skip-error are not tagged automatically.

Step 2 — Review matches

Check that key versions point at sensible commits, for example:

Version	Expected commit	Source
2.7.1	7e93418	manual / fingerprint
2.7.0	f81d3c4	manual / fingerprint
2.6.9	dceffbe	manual / fingerprint

To backfill a subset only, set versions (e.g. 2.7.0,2.7.1) instead of relying on since.

Adjust min_score (default 0.95) if a version is skipped but looks correct in the log.

Step 3 — Apply tags

1. Run Backfill Releases again with:
   • dry_run: false
   • confirm: I-have-reviewed-the-table
2. Keep the same since / versions / min_score as the dry run you approved.

This creates annotated tags and GitHub Releases. Existing tags are skipped.

Local dry run (optional)

git fetch origin version-2
git checkout version-2
python scripts/backfill_release_tags.py --since 2.6.2

Apply locally only if you know what you are doing:

python scripts/backfill_release_tags.py --since 2.6.2 --apply --confirm I-have-reviewed-the-table

Test plan

• Merge PR
• Run Backfill Releases dry run; verify plan for 2.6.2–2.7.1
• Apply backfill with confirm gate
• Verify tags exist: git fetch --tags && git tag -l '2.7.*'
• Verify GitHub Releases page lists backfilled versions
• Test forward release on next setup.py bump (or manual Release dispatch)

[persandstrom]

Thanks for the PR! I need a bit of time to review it, since I’m not very familiar with github workflows. I’m quite occupied right now, so it may take me a few weeks to get back to you.

[rasmusbe]

No problems, let me know if you have any questions 😄
The reason I want to get release tags working is to not get comments like this in future releases