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

feat: enhance embedding model configuration and retrieval logic

- 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)

Merge origin/experiment-lab (LangChain RAG) into experiment-lab + product features

feat(experiment-lab): AI transparency bar, tenant-scoped RAG, citations, proofread/enhance fixes

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

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