Root directory cleanup, .gitignore update

[fonnesbeck]

Description

Removed files that are no longer used (RELEASE_NOTES.md and .mailmap) and added Jupyter and Claude directories to the .gitignore.

Related Issue

• Closes #
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

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📚 Documentation preview 📚: https://pymc--7775.org.readthedocs.build/en/7775/

[Copilot]

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

Files not reviewed (1)

• .mailmap: Language not supported