Notification card for sync events and quiet agent asides; position/stacking is the consumer's job (fixed bottom-right, 12px gap).

```jsx
<Toast tone="ok" title="Reconcile finished" onDismiss={hide}>
  500 issues in 3.2s. Nothing drifted.
</Toast>
<Toast tone="warn" title="Gitea unreachable">
  I'll keep trying and say nothing more about it.
</Toast>
```
