Database-aware Zubi frontend loaded

This version is wired for a backend that uses:

• database/learning_data/ for learning text files
• database/chats_data/ for persistent chat sessions
• database/vector_store/ for FAISS index storage
• userdata.txt, system_context.txt, and extra .txt files as auto-loaded context

At request time, the backend should only send top-k retrieved chunks from learning data and past chats rather than dumping full files into the prompt.