Fix file extension mismatch for CPI document - file 06 is HTML not PDF

[adisinghstudent]

Problem

File 06_bls_cpi_2025-08.pdf has a .pdf extension but is actually an HTML file, causing upload failures to OpenAI vector stores when users try to set up the Knowledge Assistant example.

Solution

• Renamed 06_bls_cpi_2025-08.pdf → 06_bls_cpi_2025-08.html
• Updated references in backend/app/documents.py
• Updated agent instructions in backend/app/assistant_agent.py
• Added bun.lock to .gitignore to prevent accidental commits

Testing

• Verified the file is HTML using the file command
• File now uploads successfully to vector stores
• Knowledge Assistant example works as expected