[maciekb]

Summary

• Add shared contributor and coding-agent guidance in AGENTS.md.
• Reuse the guidance from CLAUDE.md and document domain and issue-tracker conventions.
• Add GitHub Actions checks for Python 3.10–3.12, pytest, Ruff lint, and formatting.
• Expand README development documentation and ignore Ruff cache files.

Testing

• GitHub Actions configured to run pytest, Ruff lint, and formatting checks across Python 3.10–3.12.