[Docs] Add CHANGELOG and adopt conventional commits / semantic versioning

[kelly-musk]

Problem

There is no CHANGELOG.md and no automated release process. The commitlint.config.js enforces conventional commit messages but they do not drive automated versioning or changelog generation.

Fix

1. Add CHANGELOG.md (can be auto-generated from git history)
2. Add release-please or semantic-release GitHub Action to automate version bumping, changelog entries, and GitHub Release creation

Impact

Low DX — improves release management and communication.