docs: add comprehensive AI agent documentation

Add AGENTS.md with detailed guide for AI assistants covering:
- Project overview and technology stack
- Directory structure and organization
- Development workflows and build processes
- Code conventions and patterns
- Common tasks with examples
- Important files and their purposes
- Testing checklists and best practices

Add CLAUDE.md as a pointer to AGENTS.md for easy discovery.

https://claude.ai/code/session_01KDy8pf9zKwVCYA24Uw11Uq

Author: claude