ci: restore changelog updates

[bearomorphism]

Description

The release workflow stopped committing CHANGELOG.md after migrating from commitizen-action to setup-cz, because the replacement configuration no longer enabled changelog updates during cz bump. GitHub release notes continued to be generated into a temporary file, leaving the repository changelog stale after v4.13.9.

This enables changelog generation on bump, uses incremental generation to preserve historical manual edits, and backfills all 13 releases from v4.13.10 through v4.18.0. It also documents release-triggering Conventional Commit and PR title types for AI agents to prevent CI-only changes from causing patch releases.

Checklist

• I have read the contributing guidelines

Was generative AI tooling used to co-author this PR?

• Yes (GitHub Copilot)

Generated-by: GitHub Copilot following the guidelines

Code Changes

• Add test cases to all the changes you introduce (N/A: workflow/configuration change covered by existing bump and changelog tests)
• Run uv run poe all locally to ensure this change passes linter check and tests
• Manually test the changes:
  • Verify the feature/bug fix works as expected in real-world scenarios
  • Test edge cases and error conditions
  • Ensure backward compatibility is maintained
  • Document any manual testing steps performed
• Update the documentation for the changes

Documentation Changes

The repository changelog is backfilled from the existing release tags, and AGENTS.md now explains which commit and PR title types trigger releases.

• Run uv run poe doc locally to ensure the documentation pages renders correctly (N/A)
• Check and fix any broken links (internal or external) (N/A)

Expected Behavior

Each successful automated version bump commits the new changelog entry to CHANGELOG.md. Incremental generation updates only releases newer than the latest version already present.

Steps to Test This Pull Request

1. Run uv run cz changelog --incremental twice and confirm the second run leaves CHANGELOG.md unchanged.
2. Run uv run cz bump --dry-run --yes --increment patch and confirm the configured changelog-enabled bump is previewed.
3. Run uv run pytest -q tests/commands/test_bump_command.py tests/commands/test_changelog_command.py.
4. Run uv run prek run check-yaml --files .github/workflows/bumpversion.yml.

Additional Context

The regression was introduced in PR #1924 by commit 97fb356d, which replaced commitizen-action (defaulting to --changelog) with a direct cz bump --yes invocation without the equivalent configuration.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.26%. Comparing base (d910b66) to head (c391d9d).
⚠️ Report is 3 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2074   +/-   ##
=======================================
  Coverage   98.26%   98.26%           
=======================================
  Files          61       61           
  Lines        2829     2829           
=======================================
  Hits         2780     2780           
  Misses         49       49           

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[bearomorphism]

Thanks for quick review! (I'm still reading the root cause analysis from AI)

[github-actions]

🔍 Commitizen bump preview

No commits in this PR are eligible for a version bump.