Add initial guide for AI agents

[djhoese]

Mostly written by Claude, but modified by me.

• Closes #xxxx (remove if there is no corresponding issue, which should only be the case for minor changes)
• Tests added (for all bug fixes or enhancements)
• Tests passed (for all non-documentation changes)
• Passes git diff origin/master **/*py | flake8 --diff (remove if you did not edit any Python files)
• Fully documented (remove if this change should not be visible to users, e.g., if it is an internal clean-up, or if this is part of a larger project that will be documented later)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.04%. Comparing base (ec5ff66) to head (5b328cf).
⚠️ Report is 42 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #235      +/-   ##
==========================================
- Coverage   92.06%   92.04%   -0.03%     
==========================================
  Files          12       12              
  Lines        4161     4161              
==========================================
- Hits         3831     3830       -1     
- Misses        330      331       +1     

Flag	Coverage Δ
unittests	92.04% <ø> (-0.03%)	⬇️

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[pnuu]

LGTM