Update cookbook plan: Mark Notebook 2 as complete with cleanup
- Mark Notebook 2 (Financial Applications) as complete
- Document cleanup and polish work done on 2025-10-15
- Update status to reflect Notebook 2 completion
- Document improvements: fixed cell types, added missing code, enhanced flow
- Update next steps for Notebook 3 development
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Co-Authored-By: Claude <noreply@anthropic.com>