5-step quality improvement: SentenceTransformer embeddings, better system prompt, rich sources, TOP_K=4, deduplication

Replace Gemini with NVIDIA Mistral API

Use gemini-2.0-flash-lite (same as PharmAvenir - proven working model)

Switch back to google-generativeai (gemini-pro) with new API key

Switch LLM from Gemini to Groq (openai/gpt-oss-120b)

Fix: read GEMINI_API_KEY from environment (HF Spaces secret)

Initial commit: Pharmaand RAG backend