Align the project with AI contribution standards

It would be good to add some skills here to help enforce our standards, as well as an `AGENTS.md` file.

## Description / Proposal

Add `AGENTS.md` and `.agents/skills` to align the project with AI-assisted contribution standards.

This would help:
- document repository rules
- check whether changes follow those rules
- improve code reviews
- help maintainers and contributors stay aligned with project standards

## References
- Kubebuilder agents: https://github.com/kubernetes-sigs/kubebuilder/tree/master/.agents/skills
- Kubebuilder AGENTS.md: https://github.com/kubernetes-sigs/kubebuilder/blob/master/AGENTS.md
- Agent Skills: https://agentskills.io/home
- AGENTS.md: https://agents.md/

Start by reviewing the referenced Kubebuilder AGENTS.md and .agents/skills examples, along with the Agent Skills and AGENTS.md guidance. Add AGENTS.md and .agents/skills for controller-tools, documenting repository rules and checks that align contributions with the project’s standards.

Written by the indexing model from the issue text.