Notification Playground :)

Open the bell icon to see polling, optimistic updates, and filters in action.

1. Scenario starts with 12 notifications and keeps adding more over time.
2. Open the bell panel.
3. Click mark-as-read on any unread notification.
4. Wait for the next poll (about 2.5s): it can flip back to unread.
5. Wait one more poll: it returns to read when the server write lands.