feat(qa): Remove document filtering from Q&A queries

feat(documents): Add cache invalidation on document deletion

docs: Expand documentation and add LLM chunking configuration

feat: Implement a complete Q&A system including document processing, chunking, embeddings, and retrieval-augmented generation.

feat: Implement core backend services including user authentication, Q&A, conversation history, and document management with associated database schemas and API endpoints.

Add initial project dependencies to requirements.txt

implement initial RAG-based document Q&A backend API.