Auto-update CHANGELOG.md on release

[RAprogramm]

Problem

Currently auto-release.yml generates changelog using git-cliff and adds it to GitHub release body, but CHANGELOG.md file in the repository is not updated automatically.

Expected Behavior

After each successful release, CHANGELOG.md should be automatically updated with:

1. New version section with all changes from that release
2. Fresh [unreleased] section for upcoming changes
3. Proper version comparison links in footer

Implementation

Add a step to auto-release.yml after GitHub release creation:

1. Generate full CHANGELOG.md using git-cliff
2. Commit updated CHANGELOG.md back to main branch
3. Use [skip ci] to avoid triggering CI again

References

• git-cliff docs: https://git-cliff.org/docs/
• Current config: cliff.toml
• Auto-release workflow: .github/workflows/auto-release.yml