Radio for one-of choices ("deadline: hard or soft?" — Reginald asks at milestone creation).

```jsx
<Radio name="deadline" value="hard" label="Hard — the date matters more than the scope" checked={d === 'hard'} onChange={set} />
<Radio name="deadline" value="soft" label="Soft — the scope matters more than the date" checked={d === 'soft'} onChange={set} />
```
