fix(critical): Replace Graph API simulation with real Microsoft Graph API calls

- Implement real file upload using PUT request for small files (<4MB)
- Add upload session support for large files (>=4MB) with chunked upload
- Replace simulated metadata update with PATCH request to listItem/fields
- Implement real library statistics using Graph API queries
- Add proper error handling and logging for all operations
- Remove all asyncio.sleep() simulation calls

Resolves: openai#1 (CRITICAL priority)
Impact: Enables production deployment with real SharePoint integration

Author: User