Update out-of-date AI usage guidelines in CONTRIBUTING.md

[dd32]

Description

Updates the AI section of CONTRIBUTING.md to align with the WordPress AI Guidelines.

The previous wording in CONTRIBUTING.md (added in #2598) flatly prohibited AI-generated contributions and treated them as a potential Code of Conduct violation. That language predates and conflicts with the project-wide AI guidelines that have since been published, which permit AI-assisted contributions provided the contributor discloses their use and takes responsibility for the output.

This PR replaces the prohibition with a "Use of AI Tools" section asking contributors to disclose tooling and the extent of AI authorship, and links out to the WordPress AI Guidelines for the canonical policy.

Any discussion related to the validity of the guidelines themselves should be directed to the AI team via https://make.wordpress.org/ai/2026/02/01/ai-guidelines-for-wordpress/ or #core-ai on Slack.

Partially reverts #2598.

Suggested changelog entry

Welcome the usage of AI tools.

Related issues/external references

Related: #2722 (comment)
Partially supersedes #2724

[GaryJones]

While I think there could be scope to add more that might help defer AI slop (if needed), I'm good with this PR as it stands. We haven't had any PRs opened with slop recently that I've seen - not sure whether the previous ban wording dissuaded that.

The AI models are continually getting better, and while all PRs for this project still need a human review (time commitment, like always), I think the previously obvious lines between "AI wrote this" and "A human wrote this" are blurring to the point where the AI tool becomes exactly that - just a tool.

[jrfnl]

Just FYI: I have very strong opinions about (against) this PR, but it will take me a little while to find the time to write my thoughts up properly.

Please bear with me.