OMS-v2 Proof of Concept — Extended all-markets shared stream

Endpoints:
  GET /health          — DO health snapshot
  GET /markets         — list all tracked markets (top-of-book + stats)
  GET /book/{market}   — top-10 orderbook for a specific market

Data is held in memory only (no persistence). See
  deploy/cf-containers/proof-of-concept/README.md