chore(release): generate concise release notes per feature or area

- Rewrite polish prompt to default to inline items, nesting only for several distinct changes
- Add length/density example and drop internal details from release bodies
- Tell prerelease mode to shorten long baseline bullets
- Update changes/README.md and prompt assertions in tests

changes/README.md

@@ -42,7 +42,7 @@ How fragments turn into a release:
 
 - At release time, `bun run changelog:build` (and `bun run changelog:prerelease-notes`) pipes every pending fragment through `claude -p` to merge related items, drop noise, and rewrite into a clean user-facing release body. Write fragments as raw, informative notes — don't worry about polished prose, deduping across PRs, or line-by-line phrasing. The polish step handles all of that.
 - The polish step treats pending fragments as the final release outcome, not prerelease history. If a feature is added and then renamed or fixed before the stable cut, ship the final feature bullet instead of separate prerelease-only breaking/fix entries.
-- `CHANGELOG.md`, GitHub release notes, and prerelease notes all use short top-level items with one nested bullet per distinct change, instead of packing a release's worth of detail into a single paragraph bullet. An item with only one thing to say stays inline on the top-level bullet. Release notes and prerelease notes additionally cover user benefit and any useful action note in their nested bullets.
+- `CHANGELOG.md`, GitHub release notes, and prerelease notes all use one item per feature or area, inline by default: `- **Name**: one or two short sentences.` Items with several separate changes may use a few short nested bullets instead of a run-on sentence. Items say what changed and how to reach it; implementation details, edge cases, and step-by-step usage belong in the docs, not the release body.
 - `internal` fragments stay in `CHANGELOG.md` (inside a collapsed `<details>` block) but are dropped from the GitHub release notes entirely.
 - The polished `CHANGELOG.md` and `release/release-notes.md` are committed and reviewed before tagging — edit the Markdown by hand if Claude misses something.
 

changes/concise-release-notes.md

@@ -0,0 +1,4 @@
+type: internal
+area: release
+
+- Release notes, prerelease notes, and `CHANGELOG.md` are now generated as short items per feature or area, nesting only when an item has several separate changes.