fix(dcl): route native alarm subscribe/unsubscribe through DataConnectionManagerActor

The NativeAlarmActor sends SubscribeAlarmsRequest to the DCL manager, but the
manager only routed tag/write/browse messages to the per-connection
DataConnectionActor — alarm subscribe/unsubscribe were unhandled and dead-lettered,
so native alarms never subscribed at runtime. Caught by live T28 deployment.
Mirrors the existing HandleRoute forwarding.

tests/ZB.MOM.WW.ScadaBridge.DataConnectionLayer.Tests/DataConnectionManagerActorTests.cs

@@ -58,6 +58,23 @@ public class DataConnectionManagerActorTests : TestKit
         Assert.Contains("Unknown connection", response.ErrorMessage);
     }
 
+    [Fact]
+    public void SubscribeAlarmsToUnknownConnection_ReturnsError()
+    {
+        // Regression for the live integration gap: the NativeAlarmActor sends
+        // SubscribeAlarmsRequest to the DCL manager, which must route it to the
+        // named connection actor (or reply with an error) — not dead-letter it.
+        var manager = Sys.ActorOf(Props.Create(() =>
+            new DataConnectionManagerActor(_mockFactory, _options, _mockHealthCollector)));
+
+        manager.Tell(new SubscribeAlarmsRequest(
+            "corr1", "inst1", "nonexistent", "ns=2;s=Tank01", null, DateTimeOffset.UtcNow));
+
+        var response = ExpectMsg<SubscribeAlarmsResponse>();
+        Assert.False(response.Success);
+        Assert.Contains("Unknown connection", response.ErrorMessage);
+    }
+
     [Fact]
     public async Task DCL002_ConnectionActorCrash_PreservesSubscriptionState()
     {