ci: seed GitHub Releases with the changelog entry

Use the matching CHANGELOG.md section as the release notes and still
append GitHub's generated PR list so tagged publishes match v2.5.0-style
history without requiring a manual GitHub UI draft.

Co-authored-by: Yukai Huang <hi@yukai.dev>

Author: cursoragent

.github/workflows/publish.yml

@@ -50,12 +50,19 @@ jobs:
           GH_TOKEN: ${{ github.token }}
         run: |
           TAG="${GITHUB_REF_NAME}"
+          VERSION="${TAG#v}"
           if gh release view "$TAG" >/dev/null 2>&1; then
             echo "GitHub release ${TAG} already exists, skipping"
             exit 0
           fi
+          NOTES="$(awk -v ver="$VERSION" '
+            $0 == "## " ver {p=1; next}
+            p && /^## / {exit}
+            p
+          ' CHANGELOG.md)"
           gh release create "$TAG" \
             --title "$TAG" \
+            --notes "$NOTES" \
             --generate-notes \
             --latest