fix: Fixes for render deploy

fix: lazy import for ChromaDB compatibility on Render

feat: hybrid RAG complete, avg overall 0.600→0.612, B404 relevancy 34%→74%

feat: hybrid RAG retrieval — BM25 + vector fusion with query expansion and metadata filtering, B404 relevance 34%→74%

feat: agentic pipeline complete, 5-step deterministic workflow with RAG-enriched KB queries

feat: complete RAG-augmented LLM pipeline, all findings explained including real CVEs