feat: persistent question caching and track token usage

fix: streaming chat response logic and shared interface definitions

feat: implement streaming RAG chat endpoint and frontend integration with Groq LLM

feat: implement BM25 search index and integrate chat interface with document management API

fix: ChromaDB vector store integration with document management API and frontend upload UI

feat: initialize frontend project and implement PDF upload functionality with React Query

feat: initialize frontend project with React, Vite, Tailwind CSS, and shadcn/ui components

feat: initialize project scaffolding with hybrid RAG pipeline and frontend UI structure