feat: add CLI debug snapshot command for one-shot instance state inspection

Adds `debug snapshot --id <int>` to query a running instance's current
attribute values and alarm states without the subscribe/stream overhead
of the debug view. Routes through ManagementActor → CommunicationService
→ site DeploymentManager → InstanceActor using the existing remote query
pattern.

src/ScadaLink.SiteRuntime/Actors/DeploymentManagerActor.cs

@@ -71,6 +71,7 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         // Debug View — route to Instance Actors
         Receive<SubscribeDebugViewRequest>(RouteDebugViewSubscribe);
         Receive<UnsubscribeDebugViewRequest>(RouteDebugViewUnsubscribe);
+        Receive<DebugSnapshotRequest>(RouteDebugSnapshot);
 
         // Internal startup messages
         Receive<StartupConfigsLoaded>(HandleStartupConfigsLoaded);
@@ -453,6 +454,22 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         }
     }
 
+    private void RouteDebugSnapshot(DebugSnapshotRequest request)
+    {
+        if (_instanceActors.TryGetValue(request.InstanceUniqueName, out var instanceActor))
+        {
+            instanceActor.Forward(request);
+        }
+        else
+        {
+            _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));
+        }
+    }
+
     /// <summary>
     /// WP-33: Handles system-wide artifact deployment (shared scripts, external systems, etc.).
     /// Persists artifacts to SiteStorageService and recompiles shared scripts.