feat: add release workflow with CHANGELOG generation

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Summary

• Adds gh-release.yml triggered on pushes to main that touch source files
• Adds commit-and-tag-version as a dev dependency with commit/tag skipped (workflow handles those)
• On release: bumps version in package.json, generates categorized CHANGELOG.md, commits both back to main, then creates a GitHub Release using the latest CHANGELOG section as the release body

Why

GitHub's auto-generated release notes are a flat list of PR titles in merge order. The CHANGELOG groups changes by type (Features, Bug Fixes, CI, etc.) giving users a much cleaner upgrade story.

Test plan

• Merge this PR
• Verify the workflow triggers and creates a GitHub Release
• Check that the release body contains categorized notes from CHANGELOG.md
• Verify CHANGELOG.md is committed back to main

[flo-kn]

Tested locally