* docs: add AGENTS.md with contribution rules for AI agents
Adds a model-neutral AGENTS.md at the repo root summarizing the
conventions that most often trip up automated contributors, most
importantly that algorithms-keeper closes any PR without a checked
box in the 'Describe your change' section. Complements CONTRIBUTING.md.
* docs: use uvx/uv commands in AGENTS.md (this repo uses uv, not requirements.txt)
