OCEAN APP MASTER simulator
  GET /ws/<channels>?id=<client>&role=<role>  WebSocket  (e.g. /ws/bdc-1?id=BDC-1&role=bdc)
  GET /ws?id=<client>&role=<role>&channels=<csv>  WebSocket  (query form)
  GET /state   JSON snapshot (presence, tags, mode, events)
  POST /reset  wipe tags + events