Upload With Kb Creation

Create a new knowledge base with either file upload or markdown content.

This endpoint supports two modes:

1. File Upload: Provide 'file' parameter with document (PDF, DOCX, MD, TXT)
2. Markdown Content: Provide 'markdown_content' parameter with markdown text

Process:

1. Validates and uploads content to S3
2. Creates a new knowledge base
3. Creates a document record (version 1)
4. Returns KB and document info for async processing

The document processing (chunking, vectorization) happens asynchronously via Celery.

Note: You must provide either 'file' OR 'markdown_content', but not both.