Align Cursor rules with AGENTS.md

[drbenvincent]

Summary

• point Cursor rules to AGENTS.md as the canonical guidance
• keep Cursor-specific reminders for marimo and pre-commit workflows

Test plan

• not run (docs/rules-only change)

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📚 Documentation preview 📚: https://causalpy--673.org.readthedocs.build/en/673/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.35%. Comparing base (fed2b5c) to head (399ffc9).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #673   +/-   ##
=======================================
  Coverage   94.35%   94.35%           
=======================================
  Files          44       44           
  Lines        7517     7517           
  Branches      456      456           
=======================================
  Hits         7093     7093           
  Misses        262      262           
  Partials      162      162           

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[drbenvincent]

Putting this on hold, will probably close. I think it's superseded by #675