Add CausalPy skills and command documentation

[cetagostini]

Introduced new skill files for designing experiments, loading datasets, performing causal analysis, and working with marimo notebooks under .claude/skills/. Added detailed reference documentation for DiD, ITS, and Synthetic Control methods. Added .cursor/commands/ files covering CausalPy demos, estimators, extras (including PlaceboAnalysis), marimo usage, methods, and research guidance. Updated .gitignore and pyproject.toml to support these additions.

---

📚 Documentation preview 📚: https://causalpy--589.org.readthedocs.build/en/589/

[cursor]

PR Summary

Adds comprehensive CausalPy skills and Cursor command docs (DiD/ITS/SC, datasets, placebo analysis, marimo) and updates env/gitignore with marimo runtime config.

• Docs/Skills:
  • Add CausalPy skills in .claude/skills/ for method selection, dataset loading, causal analysis (with DiD/ITS/SC references), placebo-in-time analysis (with full PlaceboAnalysis implementation), and marimo workflow/best-practices.
• Cursor Commands:
  • Add .cursor/commands/ docs for demos, estimators, methods, extras (PlaceboAnalysis), marimo usage, research/planning/implementation, and committing workflows.
• Tooling/Config:
  • Update .gitignore to ignore .cursor/plans and .marimo/.
  • Add "marimo[mcp]" to environment.yml.
  • Configure marimo autorun in pyproject.toml ([tool.marimo.runtime]).

^{Written by Cursor Bugbot for commit f6a9d0b. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.21%. Comparing base (8e672f2) to head (f6a9d0b).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #589   +/-   ##
=======================================
  Coverage   93.21%   93.21%           
=======================================
  Files          35       35           
  Lines        5511     5511           
  Branches      358      358           
=======================================
  Hits         5137     5137           
  Misses        246      246           
  Partials      128      128           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[drbenvincent]

Just realised that we've got an issue that this PR probably solves #563

Will try to review soon. Didn't manage to do it today because of a work deadline.

[drbenvincent]

There is no placebo in time PR or functionality in main at the moment. So that skill will only work for you I imagine @cetagostini. But I will not treat that as blocking. Will approve so you can proceed 🏃🏻