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.CentralUI/Components/Pages/Deployment/DebugView.razor

@@ -445,6 +445,18 @@
                     });
                 });
 
+            // M2.11: the site returns InstanceNotFound=true when the instance is
+            // not deployed there (e.g. deployment not yet pushed, or wrong site).
+            if (session.InitialSnapshot.InstanceNotFound)
+            {
+                DebugStreamService.StopStream(session.SessionId);
+                _toast.ShowError(
+                    $"Instance is not deployed on that site. " +
+                    $"Deploy it first or choose the correct site.");
+                _connecting = false;
+                return;
+            }
+
             _session = session;
 
             // Populate initial state from snapshot