feat: wire all health metrics and add instance counts to dashboard

Wired ISiteHealthCollector calls for script errors (ScriptExecutionActor),
alarm eval errors (AlarmActor), dead letters (DeadLetterMonitorActor), and
S&F buffer depth placeholder. Added instance count tracking (deployed/
enabled/disabled) to SiteHealthReport via DeploymentManagerActor. Updated
Health Dashboard UI to show instance counts per site. All metrics flow
through the existing health report pipeline via ClusterClient.

tests/ScadaLink.Commons.Tests/Messages/MessageConventionTests.cs

@@ -98,7 +98,7 @@ public class MessageConventionTests
             },
             0, 0,
             new Dictionary<string, int> { ["queue1"] = 5 },
-            0);
+            0, 0, 0, 0);
 
         var json = JsonSerializer.Serialize(msg);
         var deserialized = JsonSerializer.Deserialize<ScadaLink.Commons.Messages.Health.SiteHealthReport>(json);