Many display countdowns

Use one shared useTimer() when rows only need countdown labels.

Many display-only countdownsLive

Display-only list

4 countdowns

idle

Lot 100:12 left

Lot 200:24 left

Lot 300:36 left

Lot 400:48 left

One shared `useTimer()` drives every display-only row.

const clock = useTimer({ autoStart: true, updateIntervalMs: 1000 });
const remainingMs = Math.max(0, item.expiresAt - clock.now);