test(communication): M2.11 review nits — bridge-actor not-found test + dead-letter comment + toast wording (#24)

- Add DebugStreamBridgeActorTests: On_InstanceNotFound_Snapshot_Forwards_To_OnEvent_Does_Not_Open_Stream_And_Terminates — asserts _onEvent receives the not-found snapshot, SubscribeCalls remains empty, and the actor terminates cleanly via Watch/ExpectTerminated.
- Add comment in DebugStreamBridgeActor near Context.Stop(Self) explaining that the subsequent StopDebugStream Tell from DebugStreamService.StopStream produces a benign expected dead-letter.
- Reword not-found toast in DebugView.razor to "Instance not found on the selected site — check the deployment target." (accurate when the instance may be deployed to a different site).

src/ZB.MOM.WW.ScadaBridge.Communication/Actors/DebugStreamBridgeActor.cs

@@ -98,6 +98,10 @@ public class DebugStreamBridgeActor : ReceiveActor, IWithTimers
                     _instanceUniqueName);
                 _stopped = true;
                 _onEvent(snapshot); // resolves the snapshot TCS with InstanceNotFound=true
+                // Note: after Context.Stop(Self) below the actor is dead. DebugStreamService
+                // inspects InitialSnapshot.InstanceNotFound and calls StopStream, which sends
+                // a StopDebugStream message. That Tell arrives after the actor has already
+                // stopped, producing a benign Akka dead-letter — expected and harmless.
                 Context.Stop(Self);
                 return;
             }