fix(release): repair the 5.1.0 changelog, PR body and draft notes

[derrickmehaffy]

#219 broke the changelog in #217. Every section renders as two lists with a gap
down the middle:

### 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)
                          ← blank line ends the list
* **admin:** make the panel work in a production build, and test it (#184)
* await the cache purge instead of deferring it to onCommit

The consolidation joined the two runs of entries with a separator:

existing.entries = [...trimBlank(existing.entries), '', ...trimBlank(group.entries)];

A blank line inside a markdown list ends it. Removed, and both runs are stripped
of blank lines before joining.

I said that change was verified. It wasn't.

I checked entry counts (36 = 3 + 33), heading order, and the maximum run of
consecutive blank lines. None of those can see a single blank line between two
list items — the count is right, the order is right, and the run length is 1.

The check that finds it looks for exactly that shape, and now runs against the
output:

=== blank line between two '* ' entries ===
  line 234  ← 4.0.0-alpha.0, present in the input, deliberately untouched

Zero new splits; the 5.1.0 section is one contiguous list per subsection:

### Features
* add a cache statistics endpoint for the admin dashboard
* add an opt-in content API purge endpoint
* **admin:** rewrite the admin panel in TypeScript and add a dashboard (#181)
…

The already-broken branch

release-please regenerates CHANGELOG.md on the release branch from main on
each run, so once this lands the next run rebuilds it and the fixed fold applies.
I will confirm that on #217 rather than assume it — and if the branch does not
regenerate, deleting it makes release-please recreate it cleanly.

🤖 Generated with Claude Code