Add Codex change review command

[goonobu-dot]

Summary

• Add codex-maintainer-kit review to generate CODEX_REVIEW.md from current working-tree changes.
• Classify changed files into docs, tests, source, config, CI, and security-sensitive categories.
• Generate risk level, maintainer checklist, verification commands, and a suggested Codex review prompt.
• Document the review step in README and add an example report.

Test Plan

• python3 -m pytest -p no:cacheprovider tests -q
• PYTHONPATH=src python3 -m codex_maintainer_kit.cli review . --output /tmp/codex-review.md