Release notes written from the commits since the previous tag

- The release page's "What's new" now comes from each commit's subject and body since the
  previous tag, without trailers or any line naming the assistant that helped write them.
- `tools/release.sh notes` writes the notes alone; the release checkout fetches the tags.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

.gitea/workflows/release.yml

@@ -16,6 +16,8 @@ jobs:
     runs-on: nuvola
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
 
       - name: Prepare
         run: .gitea/scripts/prepare.sh