chore: add CLAUDE.md with repo guidance for AI assistants

[mbates]

Summary

• Adds CLAUDE.md with repo structure, commands, conventions, and PR/commit rules for AI assistants.
• Removes CLAUDE.md from .gitignore so it can be tracked.

Test plan

• No code changes; docs/config only.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.18%. Comparing base (e8b175f) to head (7fc2afe).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #62   +/-   ##
=======================================
  Coverage   97.18%   97.18%           
=======================================
  Files          17       17           
  Lines         853      853           
  Branches      244      244           
=======================================
  Hits          829      829           
  Misses          1        1           
  Partials       23       23           

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[github-actions]

🎉 This PR is included in version 1.10.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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