feat: add git-cliff changelog generation

[miguelgila]

Summary

• Add cliff.toml configuration for git-cliff with conventional commit parsing and categorized sections (Features, Bug Fixes, Performance, Refactoring, Documentation, Testing, CI/CD, Reverts, Miscellaneous)
• Integrate git-cliff into auto-release.yml and manual-release.yml to update CHANGELOG.md on each release commit
• Replace GitHub's generate_release_notes: true in release.yml with git-cliff output for structured release notes on GitHub Releases
• Generate initial CHANGELOG.md from existing commit history

Test plan

• Verify manual-release.yml dry-run shows CHANGELOG.md in the diff
• Trigger a manual release and confirm CHANGELOG.md is updated in the release commit
• Confirm GitHub Release page shows categorized release notes from git-cliff

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.20%. Comparing base (29262c2) to head (adbd747).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #18   +/-   ##
=======================================
  Coverage   86.20%   86.20%           
=======================================
  Files           4        4           
  Lines         174      174           
=======================================
  Hits          150      150           
  Misses         24       24           

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