fix(siteruntime): M2.11 — unknown-instance debug snapshot returns InstanceNotFound=true (#24)

RouteDebugSnapshot and RouteDebugViewSubscribe on DeploymentManagerActor
previously returned an empty DebugViewSnapshot for unknown instances,
indistinguishable from a deployed-but-empty instance. Callers had no way
to differentiate "not deployed here" from "deployed, no data yet."

Approach — additive field on existing message contract:
  Added `bool InstanceNotFound = false` as an optional trailing parameter
  to DebugViewSnapshot (Commons). All existing positional constructor calls
  and serialized wire frames are unaffected (default = false). A dedicated
  new message type was considered but rejected: the ClusterClient channel
  and DebugStreamService TCS are already typed on DebugViewSnapshot, and a
  second reply union would require wider changes for zero additive-safety
  gain.

Changes:
  - Commons/DebugViewSnapshot: add InstanceNotFound = false (additive)
  - DeploymentManagerActor: set InstanceNotFound=true in both unknown-
    instance branches (RouteDebugViewSubscribe, RouteDebugSnapshot)
  - DebugStreamBridgeActor: when snapshot.InstanceNotFound, forward it to
    _onEvent (resolves the TCS) then stop cleanly; no gRPC stream opened
  - DebugView.razor: check session.InitialSnapshot.InstanceNotFound after
    connect and show a clear "not deployed on this site" error toast
  - 3 new tests in DeploymentManagerActorTests covering: unknown→snapshot,
    unknown→subscribe, known-empty→InstanceNotFound stays false

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

@@ -85,9 +85,23 @@ public class DebugStreamBridgeActor : ReceiveActor, IWithTimers
         _grpcNodeAAddress = grpcNodeAAddress;
         _grpcNodeBAddress = grpcNodeBAddress;
 
-        // Initial snapshot response from the site (via ClusterClient)
+        // Initial snapshot response from the site (via ClusterClient).
+        // M2.11: if the site reports InstanceNotFound=true the instance is not
+        // deployed there.  Forward the snapshot (with InstanceNotFound=true) to
+        // _onEvent so DebugStreamService's TCS resolves and the caller can
+        // inspect the flag; then stop cleanly without opening a gRPC stream.
         Receive<DebugViewSnapshot>(snapshot =>
         {
+            if (snapshot.InstanceNotFound)
+            {
+                _log.Warning("Instance {0} is not deployed on site; terminating debug stream",
+                    _instanceUniqueName);
+                _stopped = true;
+                _onEvent(snapshot); // resolves the snapshot TCS with InstanceNotFound=true
+                Context.Stop(Self);
+                return;
+            }
+
             _log.Info("Received initial snapshot for {0} ({1} attrs, {2} alarms)",
                 _instanceUniqueName, snapshot.AttributeValues.Count, snapshot.AlarmStates.Count);
             _onEvent(snapshot);