ci: take the release page's prose from the CHANGELOG too

[gloryfromca]

Summary

Follow-up to #389. That PR left two things to be written at publish time — the lead summary and the upgrade notes — which is the worst moment for it: the changes are weeks old by then and the text gets no review. Both belong in the CHANGELOG entry the release PR is already editing.

• The lead needed no code. Text between ## [X.Y.Z] and the first ### group already flowed into the page; it was just never documented, so nobody wrote it there.
• The Upgrade group did. CI appended its own ## Upgrade, so a CHANGELOG carrying upgrade notes produced two headings. The group is now lifted out of the extracted body and the boilerplate wrapped around it — pip line above, prose in the middle, compare link below — which is the shape of every release page since 1.1.3.

Publishing becomes a read-through and a click.

Area

• CI, build, or release

Verification

Extraction re-run from the workflow YAML against a fixture repo (CHANGELOG with a lead paragraph and an ### Upgrade group, tags v1.2.2 / v1.3.0) and against the real CHANGELOG.md:

fixture v1.3.0  rc=0
  lead paragraph, verbatim, above the first heading
  ## Added / ## Fixed
  ## Upgrade -> pip block, then the CHANGELOG's upgrade prose, then
                **Full changelog:** [v1.2.2...v1.3.0](...)
  one "## Upgrade" heading, not two

fixture v1.2.2  rc=0   no lead, no Upgrade group -> pip block only
real    v1.2.2  rc=0   ## Added / ## Changed / ## Fixed / ## Docs / ## Upgrade
                       one "## Upgrade" heading

Output for the fixture matches the hand-written v1.2.1 page section for section.

Checklist

• I kept the change scoped to the relevant area.
• I am opening this from a separate branch, not pushing directly to main.
• I updated docs, examples, or setup notes when behavior changed.
• I added or updated tests when the change affects behavior.
• I did not commit secrets, .env files, dependency folders, or generated output.
• Active relative links in Markdown files resolve.

Notes for Reviewers

The /release skill now shows the CHANGELOG entry as the source of the page and says to omit the ### Upgrade group when there is nothing to say — 1.1.4 and 1.2.0 have nothing there, and prompting for filler is how a section becomes noise.

Still unverified end to end: the job has never run on a real tag push. Same open question as #389 — an rc tag would settle it.

🤖 Generated with Claude Code