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/InstanceActor.cs

@@ -8,6 +8,7 @@ using ScadaLink.Commons.Messages.ScriptExecution;
 using ScadaLink.Commons.Messages.Streaming;
 using ScadaLink.Commons.Types.Enums;
 using ScadaLink.Commons.Types.Flattening;
+using ScadaLink.HealthMonitoring;
 using ScadaLink.SiteRuntime.Persistence;
 using ScadaLink.SiteRuntime.Scripts;
 using ScadaLink.SiteRuntime.Streaming;
@@ -37,6 +38,7 @@ public class InstanceActor : ReceiveActor
     private readonly SiteStreamManager? _streamManager;
     private readonly SiteRuntimeOptions _options;
     private readonly ILogger _logger;
+    private readonly ISiteHealthCollector? _healthCollector;
     private readonly Dictionary<string, object?> _attributes = new();
     private readonly Dictionary<string, string> _attributeQualities = new();
     private readonly Dictionary<string, AlarmState> _alarmStates = new();
@@ -61,7 +63,8 @@ public class InstanceActor : ReceiveActor
         SiteStreamManager? streamManager,
         SiteRuntimeOptions options,
         ILogger logger,
-        IActorRef? dclManager = null)
+        IActorRef? dclManager = null,
+        ISiteHealthCollector? healthCollector = null)
     {
         _instanceUniqueName = instanceUniqueName;
         _storage = storage;
@@ -71,6 +74,7 @@ public class InstanceActor : ReceiveActor
         _options = options;
         _logger = logger;
         _dclManager = dclManager;
+        _healthCollector = healthCollector;
 
         // Deserialize the flattened configuration
         _configuration = JsonSerializer.Deserialize<FlattenedConfiguration>(configJson);
@@ -474,7 +478,8 @@ public class InstanceActor : ReceiveActor
                 script,
                 _sharedScriptLibrary,
                 _options,
-                _logger));
+                _logger,
+                _healthCollector));
 
             var actorRef = Context.ActorOf(props, $"script-{script.CanonicalName}");
             _scriptActors[script.CanonicalName] = actorRef;
@@ -516,7 +521,8 @@ public class InstanceActor : ReceiveActor
                 onTriggerScript,
                 _sharedScriptLibrary,
                 _options,
-                _logger));
+                _logger,
+                _healthCollector));
 
             var actorRef = Context.ActorOf(props, $"alarm-{alarm.CanonicalName}");
             _alarmActors[alarm.CanonicalName] = actorRef;