fix: only active singleton node sends health reports

Both nodes of a site cluster were sending health reports. The standby
node (without the DeploymentManager singleton) reported 0 instances and
no connections, overwriting the active node's data in the aggregator.

Added IsActiveNode flag to ISiteHealthCollector, set by
DeploymentManagerActor on PreStart/PostStop. HealthReportSender skips
sending when the node is not active. Also ensured EnsureDclConnections
is called during startup batch creation so data connections survive
container restarts.

src/ScadaLink.SiteRuntime/Actors/DeploymentManagerActor.cs

@@ -83,6 +83,7 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
     protected override void PreStart()
     {
         base.PreStart();
+        _healthCollector?.SetActiveNode(true);
         _logger.LogInformation("DeploymentManagerActor starting — loading deployed configs from SQLite...");
 
         // Load all configs asynchronously and pipe to self
@@ -94,6 +95,12 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         }).PipeTo(Self);
     }
 
+    protected override void PostStop()
+    {
+        _healthCollector?.SetActiveNode(false);
+        base.PostStop();
+    }
+
     /// <summary>
     /// OneForOneStrategy: Resume on exceptions to preserve Instance Actor state,
     /// Stop only on ActorInitializationException (actor failed to start).
@@ -160,6 +167,7 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         for (var i = startIdx; i < endIdx; i++)
         {
             var config = state.Configs[i];
+            EnsureDclConnections(config.ConfigJson);
             CreateInstanceActor(config.InstanceUniqueName, config.ConfigJson);
         }