docs: add comprehensive agent documentation (#8)

Add AGENTS.md with detailed documentation for AI agents and developers:
- Repository overview and architecture
- Development policies (PRs, conventional commits)
- Release process with release-please
- CI/CD pipeline details
- Code standards and testing strategy
- Security practices (OIDC for PyPI)
- Common development tasks and workflows
- FAQ section

Add CLAUDE.md as a pointer to AGENTS.md for Claude-specific context loading.

This documentation ensures consistent development practices and provides
comprehensive guidance for both AI agents and human developers working
on the repository.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: mldangelo