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.SiteRuntime/Actors/DeploymentManagerActor.cs

@@ -895,11 +895,14 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         }
         else
         {
+            // M2.11: set InstanceNotFound=true so the caller can distinguish
+            // "not deployed on this site" from a deployed-but-empty instance.
             _logger.LogWarning(
                 "Debug view subscribe for unknown instance {Instance}", request.InstanceUniqueName);
             Sender.Tell(new DebugViewSnapshot(
                 request.InstanceUniqueName, Array.Empty<Commons.Messages.Streaming.AttributeValueChanged>(),
-                Array.Empty<Commons.Messages.Streaming.AlarmStateChanged>(), DateTimeOffset.UtcNow));
+                Array.Empty<Commons.Messages.Streaming.AlarmStateChanged>(), DateTimeOffset.UtcNow,
+                InstanceNotFound: true));
         }
     }
 
@@ -919,11 +922,14 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         }
         else
         {
+            // M2.11: set InstanceNotFound=true so the caller can distinguish
+            // "not deployed on this site" from a deployed-but-empty instance.
             _logger.LogWarning(
                 "Debug snapshot for unknown instance {Instance}", request.InstanceUniqueName);
             Sender.Tell(new DebugViewSnapshot(
                 request.InstanceUniqueName, Array.Empty<Commons.Messages.Streaming.AttributeValueChanged>(),
-                Array.Empty<Commons.Messages.Streaming.AlarmStateChanged>(), DateTimeOffset.UtcNow));
+                Array.Empty<Commons.Messages.Streaming.AlarmStateChanged>(), DateTimeOffset.UtcNow,
+                InstanceNotFound: true));
         }
     }