security: remove litellm (supply chain risk) + unused CLI deps, add openai

Add slowapi for rate limiting

feat: wire Groq and serve UI from backend

Add fastapi and uvicorn to requirements.txt

deepshell-backend/requirements.txt removed the unwanted

Update requirements.txt to include deepshell==1.0.0 and remove archived requirements

Restore requirements.txt for backend dependencies

Archive backend docs and tests; clean up UI repo

Convert deepshell-backend from submodule to normal folder