feat: async pipeline, job queue, generation hardening, and docs

- Added support for RICS survey levels (1, 2, 3) in document uploads and reports, allowing for better tier management and retrieval filtering.

feat: FAISS-only vector store (remove Chroma)

feat(experiment-lab): rewrite RAG pipeline using LangChain framework

fix: comprehensive codebase review fixes (critical + major + minor issues)

feat: scaffold complete RAG system for RICS-style report generation