Fix Prerequisites typo & variable reference error

[schwentker]

Summary

Fixes spelling & variable reference issues across multiple exercise notebooks that could prevent workshop completion.

Changes Made

Spelling Corrections

• "Prequisites" → "Prerequisites" in notebook headers across:
  • 2-Document_QnA_with_ask.ipynb
  • 3-Hub_QnA_with_ask.ipynb
  • 4-Flexible_extraction_with_extract copy.ipynb
  • 5-Structured_extraction_with_extract_structured copy.ipynb
  • 6-Box_agents_and_AI_APIs.ipynb

Variable Reference Fix

• File 4: Fixed undefined variable file.id → file_id in create_ai_extract call
• Prevents runtime error that would break exercise 4

Impact

• Prevents workshop failures: Eliminates undefined variable error in exercise 4
• Professional presentation: Corrects spelling errors in section headers
• User experience: Ensures smooth progression through all exercises

Files Changed

• 5 notebook files with spelling corrections
• 1 functional fix for variable reference error

Fixes #4