Create an AGENTS.md file

[priethor]

What?

This PR adds an AGENTS.md file with instructions to help AI agents work with this repository.

Why?

AI agents are becoming increasingly popular as a supporting development tool. Rather than ignoring this fact, providing guidelines for AI agents will help them be more effective, resulting in a better and faster developer experience with reduced cost and environmental impact.

How?

By following the AGENTS.md format supported by many agents. It's not a formal spec, but a de facto standard, which focuses on:

• Give agents a clear, predictable place for instructions.
• Keep READMEs concise and focused on human contributors.
• Provide precise, agent-focused guidance that complements existing README and docs.

This first iteration includes dev environment tips, testing instructions, and PR instructions.

Testing Instructions

1. Run your favorite AI agent and ask it to lint or run tests, which is something they usually don't get right on the first try

[cbravobernal]

LGTM