bug(rag): query side appends /faiss_index but ingest writes to vectordb_dir directly → KB retrieval never finds the index (#1951 follow-on)
bug(rag): query side appends /faiss_index but ingest writes to vectordb_dir directly → KB retrieval never finds the index (#1951 follow-on): ## Severity **High** — RAG retrieval is broken for the standard config path: `query_knowledge_base` returns *"no knowledge base found"* even when an index was successfully ingested. Affects any setup where ingest and que