Add the Open Home Foundation AI Policy to AI_POLICY.md file

[Hedda]

Proposed change

Adds the Open Home Foundation AI Policy to this repository. See:

• https://developers.home-assistant.io/docs/ai_policy

More details in the announced in this blog post:

• https://developers.home-assistant.io/blog/2026/07/20/ai-policy/

This is a copy of what has been rolled out to other repositories goverened by the Open Home Foundation, such as the the home-assistant and home-assistant-libs organizations:

• Adds AI_POLICY.md to the repository root.
  • The file content was copied from https://github.com/home-assistant/core/blob/dev/AI_POLICY.md
• Adds a reference to the policy in README.md
  • This text was copied from https://github.com/home-assistant/core/blob/dev/CONTRIBUTING.md#ai-policy
• Adds a reference to the policy in .github/copilot-instructions.md which AGENTS.md and CLAUDE.md symlinks to today.
• This is a documentation of the OHF policy change. It does not touch any Python code, so none of the code-related checklist options below apply.

Checklist

• The changes are tested and work correctly
• pre-commit checks pass / the code has been formatted using Black
• Tests have been added to verify that the new code works
• Device diagnostics data has been attached

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.60%. Comparing base (b139f81) to head (3421498).
⚠️ Report is 2 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #5278   +/-   ##
=======================================
  Coverage   92.60%   92.60%           
=======================================
  Files         424      424           
  Lines       14667    14667           
=======================================
  Hits        13582    13582           
  Misses       1085     1085           

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