feat(realtime): global guest-order alert on the dashboard

Guest orders from the QR/digital menu already notified via SignalR, but only
screens that were open (KDS/POS/tables) reacted — and silently (a data refresh,
no alert). So staff on any other screen never knew a menu order arrived.

- Add a global useOrderAlerts() mounted in the dashboard shell: connects to
  /hubs/kds, joins the café group, and on a new GUEST order plays a chime + shows
  a toast (localized fa/en/ar) + nudges order/KDS/POS lists to refresh — on every
  screen.
- Filter to guest QR-menu orders only (not staff POS orders): LiveOrderDto now
  carries Source, set in MapLiveOrder (+ the delivery/snappfood mappers).

86 API tests pass; dashboard tsc + build clean.

src/Meezi.API/Services/OrderService.cs

@@ -1221,5 +1221,6 @@ public class OrderService : IOrderService
             i.UnitPrice,
             i.Notes,
             i.IsVoided,
-            i.VoidedAt)).ToList());
+            i.VoidedAt)).ToList(),
+        o.Source);
 }