queen: the board and the game follow the event bus instead of redrawing every 5 s #1546

Context

Slice 3 of the epic gHashTag/t27#7718. The supervisor's event log becomes a bus (gHashTag/BrowserOS#550, spec gHashTag/t27#7800).

Today the kanban and the game redraw the whole task list every five seconds: about 1,500 tasks, around 55 KB gzipped, only to learn that one bee spoke.

Scenarios

• The board takes one snapshot, which carries its event cursor, and then reads only GET /queen/public-events?after=<cursor>&wait=25.
• What happens to each event is decided by the card events.t27 as wasm:
  • a bee heard (task.evidence) is marked heard where it is;
  • a task that moved is read again alone (issues=);
  • a gap or a pruned cursor triggers one more snapshot.
• A bee nobody hears from turns quiet with no event (bee_state of tasks.t27).
• A whole snapshot still comes every SNAPSHOT_EVERY_SECONDS, for what GitHub changed.
• A server without the bus (no cursor in the snapshot, or a 404 on the events route) is polled as before.

Acceptance criteria

• public/t27/queen/events.wasm is byte-identical to the wasm the supervisor vendors (sha256 4f568a63...).
• The trinity type ratchet does not grow.