feat(eval): RAGAS evaluation framework + RAG pipeline improvements

feat: decouple frontend + multi-turn conversation + graph explorer + CAG layer

merge: integrate HF space initial commit

feat(embedder): replace Ollama with sentence-transformers local inference

feat: Phase 4 complete — UP RERA ingestion (Rules 2016 + Regulations 2019)

feat: Phase 0 complete — RERA RAG pipeline with FastAPI