docs(changelog): roll [Unreleased] entries under [0.2.3] (#89)

0.2.3 was published to PyPI (and pyproject.toml bumped) when PRs
#85, #86, #87 landed, but the CHANGELOG entries stayed under
[Unreleased]. Moves them under a dated [0.2.3] - 2026-04-27
header and leaves a fresh empty [Unreleased] stub above for
future work. No content changes — same Fixed / Added / Changed
bullets, just under the right version heading.

Author: caohy1988

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.2.3] - 2026-04-27
+
 ### Fixed
 
 - **LLM-as-Judge AI.GENERATE path now executes against current