Resolve all high-severity architecture review findings

src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Actors/InstanceActor.cs

@@ -428,6 +428,10 @@ public class InstanceActor : ReceiveActor
     /// <inheritdoc />
     protected override void PostStop()
     {
+        foreach (var connectionName in _tagsByConnection.Keys)
+            _dclManager?.Tell(new UnsubscribeTagsRequest(
+                Guid.NewGuid().ToString("N"), _instanceUniqueName, connectionName, DateTimeOffset.UtcNow), Self);
+
         // Cancel any armed tag-subscribe watchdogs so they cannot fire after stop.
         foreach (var state in _tagSubscribeStates.Values)
             state.Timer?.Cancel();