The processing page only read dagStatus from the transcript room WS,
which loses events during page navigation and React strict mode
double-mounting (WS torn down and reconnected, historical replay
skips DAG_STATUS). Now also consumes useDagStatusMap() from
UserEventsProvider (user room), which uses a singleton WS that
survives remounts.
Priority: transcript room WS > user room WS > REST API.
Add DAG_STATUS and DAG_TASK_PROGRESS event handlers to useWebSockets
hook with exported DagTask/DagTaskStatus types. Create DagProgressTable
component with status icons, live elapsed timers, progress bars, and
expandable error rows. Wire into processing page with REST fallback.
