Previously the create-release POST sent only `{tag_name, name, draft,
prerelease}` — Gitea created the release with an empty description, so
users hitting the release page saw the tag name and nothing else.
Extracts the relevant `## [<version>]` block from CHANGELOG.md (using
$TAG with the leading `v` stripped) via awk, stopping at the next
`## [<other>]` section header or the trailing `[link-ref]: url` block,
and passes it as the `body` field to the release creation API.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>