chore(tools): add conventional-changelog-cli for automated changelog

Add `conventional-changelog-cli` and npm scripts `changelog` /
`changelog:unreleased` to generate CHANGELOG.md entries from conventional
commits. Verified `npm run changelog:unreleased` runs successfully; no
unreleased changes exist after v0.6.4, so CHANGELOG.md was not modified
in this commit.

Co-authored-by: QoderAI (Qwen 3.8 Max) <qoder_ai@qoder.com>

Author: phodal