Add `AGENTS.md` and AI usage policy by SableRaf · Pull Request #1319 · processing/processing4

SableRaf

This PR introduces:

AGENTS.md: A guide for AI-assisted coding tools (e.g., Claude, ChatGPT, Copilot) explaining how they should interact with this repository and its contributors. You can think of it as a README for coding agents.
AI_USAGE_GUIDELINES: A document for human contributors that defines what kinds of AI-assisted uses are allowed, restricted, or not permitted when contributing to this repository.
Edit: Renaming CODE-OF-CONDUCT.md to CODE_OF_CONDUCT.md for consistent naming across repositories.

Note: This is adapted from a PR already merged in p5.js.

For more background and motivation, see: processing/p5.js#8194