Wire NotificationListItem tap to deep link handler

In NotificationListItem, use an onTap callback rather than embedding navigation logic directly in the widget — keep the widget dumb. In NotificationCentreScreen, provide the onTap as: `onTap: () { if (!notification.isRead) { context.read().add(MarkNotificationRead(notification.id)); } handler.navigate(notification.payload); }`. For the visual treatment, use a conditional BoxDecoration on the item container: if `!notification.isRead`, apply a 3dp left border using the design token accent color (e.g., `AppColors.accentUnread`). For the title weight, use `isRead ?

AppTextStyles.bodyRegular : AppTextStyles.bodyBold` from the design token system. Do not store `isRead` in local widget state — derive it entirely from the BLoC state to avoid stale UI.

Write flutter_test widget tests covering: (1) tapping an unread item dispatches MarkNotificationRead before navigate is called (verify call order with a mock handler), (2) item visual state changes to read immediately after tap, (3) deep link handler called with the correct payload from the tapped notification, (4) deleted entity fallback renders snackbar without crashing, (5) malformed payload triggers fallback gracefully, (6) re-tapping a read item does not dispatch MarkNotificationRead. Use mockito or mocktail to mock NotificationDeepLinkHandler. Verify BLoC state transitions with bloc_test.