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.

src/ScadaLink.SiteRuntime/Actors/DeploymentManagerActor.cs

@@ -5,6 +5,7 @@ using ScadaLink.Commons.Messages.DebugView;
 using ScadaLink.Commons.Messages.Deployment;
 using ScadaLink.Commons.Messages.Lifecycle;
 using ScadaLink.Commons.Types.Enums;
+using ScadaLink.HealthMonitoring;
 using ScadaLink.SiteRuntime.Persistence;
 using ScadaLink.SiteRuntime.Scripts;
 using ScadaLink.SiteRuntime.Streaming;
@@ -30,7 +31,9 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
     private readonly SiteRuntimeOptions _options;
     private readonly ILogger<DeploymentManagerActor> _logger;
     private readonly IActorRef? _dclManager;
+    private readonly ISiteHealthCollector? _healthCollector;
     private readonly Dictionary<string, IActorRef> _instanceActors = new();
+    private int _totalDeployedCount;
 
     public ITimerScheduler Timers { get; set; } = null!;
 
@@ -41,7 +44,8 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         SiteStreamManager? streamManager,
         SiteRuntimeOptions options,
         ILogger<DeploymentManagerActor> logger,
-        IActorRef? dclManager = null)
+        IActorRef? dclManager = null,
+        ISiteHealthCollector? healthCollector = null)
     {
         _storage = storage;
         _compilationService = compilationService;
@@ -49,6 +53,7 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         _streamManager = streamManager;
         _options = options;
         _dclManager = dclManager;
+        _healthCollector = healthCollector;
         _logger = logger;
 
         // Lifecycle commands
@@ -123,9 +128,11 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         }
 
         var enabledConfigs = msg.Configs.Where(c => c.IsEnabled).ToList();
+        _totalDeployedCount = msg.Configs.Count;
         _logger.LogInformation(
             "Loaded {Total} deployed configs ({Enabled} enabled) from SQLite",
             msg.Configs.Count, enabledConfigs.Count);
+        UpdateInstanceCounts();
 
         if (enabledConfigs.Count == 0)
             return;
@@ -200,6 +207,8 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
 
         // Create the Instance Actor immediately (no existing actor to replace)
         CreateInstanceActor(instanceName, command.FlattenedConfigurationJson);
+        _totalDeployedCount++;
+        UpdateInstanceCounts();
 
         // Persist to SQLite and clear static overrides asynchronously
         var sender = Sender;
@@ -257,6 +266,8 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
             _instanceActors.Remove(instanceName);
         }
 
+        UpdateInstanceCounts();
+
         var sender = Sender;
         _storage.SetInstanceEnabledAsync(instanceName, false).ContinueWith(t =>
         {
@@ -313,6 +324,7 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         {
             CreateInstanceActor(instanceName, result.Config.ConfigJson);
         }
+        UpdateInstanceCounts();
 
         result.OriginalSender.Tell(new InstanceLifecycleResponse(
             result.Command.CommandId, instanceName, true, null, DateTimeOffset.UtcNow));
@@ -333,6 +345,8 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
             Context.Stop(actor);
             _instanceActors.Remove(instanceName);
         }
+        _totalDeployedCount = Math.Max(0, _totalDeployedCount - 1);
+        UpdateInstanceCounts();
 
         var sender = Sender;
         _storage.RemoveDeployedConfigAsync(instanceName).ContinueWith(t =>
@@ -536,7 +550,8 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
             _streamManager,
             _options,
             loggerFactory.CreateLogger<InstanceActor>(),
-            _dclManager));
+            _dclManager,
+            _healthCollector));
 
         var actorRef = Context.ActorOf(props, instanceName);
         _instanceActors[instanceName] = actorRef;
@@ -549,6 +564,18 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
     /// </summary>
     internal int InstanceActorCount => _instanceActors.Count;
 
+    /// <summary>
+    /// Updates the health collector with current instance counts.
+    /// Total deployed = _totalDeployedCount, enabled = running actors, disabled = difference.
+    /// </summary>
+    private void UpdateInstanceCounts()
+    {
+        _healthCollector?.SetInstanceCounts(
+            deployed: _totalDeployedCount,
+            enabled: _instanceActors.Count,
+            disabled: _totalDeployedCount - _instanceActors.Count);
+    }
+
     // ── Internal messages ──
 
     internal record StartupConfigsLoaded(List<DeployedInstance> Configs, string? Error);