Transient confirmations after an action succeeds or fails.

```jsx
<Toaster />                       // mount once, near the app root
toast.success('Agent Atlas started')
toast.error('Could not reach the gateway', { description: 'Retrying in 5s' })
```

Bottom-right, auto-dismiss ~3.5s, one line plus an optional quiet second line. Success shows a small green dot — the only hue permitted here.