Adopt a responsible Gen-AI use policy

[ilhamv]

MC/DC should adopt a clear policy for Gen-AI-assisted contributions.

Gen-AI is a valuable productivity tool, and its thoughtful use is welcome. It should support, not replace, human understanding, judgment, accountability, and collaboration.

The policy should uphold:

• Human ownership and responsibility
• Understanding of all submitted work
• Quality and respect for reviewer time
• Transparency about substantial AI assistance
• Copyright, licensing, privacy, and security
• Human-centered community and collaboration

Completion includes documenting the policy and adding a brief Gen-AI disclosure reminder to the Issue and Pull Request templates.

References: NumPy, LLVM, policy collection, and Scientific Python.