fix(release): rebuild the release PR body and draft notes from the changelog

[derrickmehaffy]

You were right and I was looking at the wrong artifact.

#217's pull request body lists 4 entries. Its changelog lists 38.

### Bug Fixes
* **admin:** stop the settings table logging a React error on every render (#215)
* **release:** fold the beta changelog into the release that supersedes it (#219)
### Documentation
* backfill 4.2.9, 5.0.0 and 5.0.1 into the changelog (#213)
### Chores
* graduate to a stable release (#218)

Why, and why it matters more than it looks

release-please generates the body from the commits since the last release —
and the last release was 5.1.0-beta. So once the beta is folded into the
changelog, the body still describes only what came after it.

github-release then copies that body into the draft release. So the
published 5.1.0 release notes would have shipped with those 4 lines, omitting
the 33 changes that are the release. Folding the changelog fixed the file and
left both of the things people actually read.

Fix

The body and the draft notes are rebuilt from CHANGELOG.md, which is the
merged and deduplicated list.

Only the text between release-please's --- delimiters is replaced; the heading
comes from the changelog, which is the shape release-please writes. That
structure is load-bearing — github-release parses the body to find the
release, and an earlier hand-edit of it is exactly why the 5.1.0-beta draft had
to be created manually.

Verified against the live #217 and its branch

version=5.1.0   changelog entries: 38
spliced 38 entries
  parses: true | version: 5.1.0 | component: undefined | entries: 38
  blank lines splitting a list in the new body: 0

The parse check runs release-please's own PullRequestBody.parse over the
rebuilt body — the check that would have caught the breakage that forced the
manual draft. Splicing twice leaves 38, so a re-run is a no-op.

🤖 Generated with Claude Code