Crew Knowledge 2.0: hybrid retrieval, retrieval lab, knowledge map canvas

Imported from GitHub issue El-SaMa/oma#148 by @El-SaMa.

Collections + agent access links, hybrid FTS+vector with RRF, reranker, contextual chunks, chunk metadata filters, per-source chunking, CAG toggle, agentic retrieval, citations; retrieval lab (eval cases, experiments, apply/rollback); React Flow knowledge map; staff + customer MCP tools; handbook. Branch feat/crew-knowledge2.