release: list one line per change in the GitHub release notes

[allen0099]

Why

The GitHub release body used to be the promoted changelog section, copied as is. Our entries explain each change in full, so the v0.3.7 release page was about 8 KB of long bullets. GitHub also turns every hard wrap into a line break, which makes the bullets even longer.

What changes

Each changelog entry now opens with a bold one-line summary:

- **Add `CacheManager.add()` for store-if-absent writes.** Details as before... ([#65](...))

scripts/changelog_release.py gets a new release_notes(). It writes the release body as one line per entry: the summary plus the issue/PR links found in that entry, grouped under the same ### headings. The body ends with a link to that version's section in the changelog on the documentation site:

### Changed

- GitHub release notes list one line per change.

**Full changelog**: https://fastapi-cachex.readthedocs.io/en/stable/changelog/#038-2026-09-26

The workflow still adds the Installation block and the "Full commit log" compare link below this, as before.

Gate

An entry without a bold summary, or a line that is neither a ### heading nor a - entry, is an error. The error message lists the offending entries. This means:

• the release job (and a dry_run) stops before it publishes anything;
• test_real_changelog_promotes, which promotes the real CHANGELOG.md, runs the same check. A pull request that adds an entry without a summary therefore fails CI, not the release.

CHANGELOG.md, docs/DEVELOPMENT.md and docs/CONTRIBUTING.md explain the format. Releases already published, and changelog entries before 0.3.8, stay as they are.

Verification

• tests/test_changelog_release.py: 25 passed, scripts/changelog_release.py at 100% coverage. The new tests cover:
  • multi-line summaries;
  • nested lists;
  • several links in one entry;
  • entries before any heading;
  • listing every entry that lacks a summary;
  • rejecting lines that are not entries;
  • main writing nothing when it refuses.
• Full suite against live Redis and Memcached: 766 passed, 100% total coverage.
• Rehearsal on a copy: promoted the real changelog and ran zensical build --strict (no issues). The #038-2026-09-26 anchor that the release notes link to exists in the built changelog page.