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/AlarmActor.cs

@@ -4,6 +4,7 @@ using Microsoft.Extensions.Logging;
 using ScadaLink.Commons.Messages.Streaming;
 using ScadaLink.Commons.Types.Enums;
 using ScadaLink.Commons.Types.Flattening;
+using ScadaLink.HealthMonitoring;
 using ScadaLink.SiteRuntime.Scripts;
 using System.Text.Json;
 
@@ -34,6 +35,7 @@ public class AlarmActor : ReceiveActor
     private readonly SharedScriptLibrary _sharedScriptLibrary;
     private readonly SiteRuntimeOptions _options;
     private readonly ILogger _logger;
+    private readonly ISiteHealthCollector? _healthCollector;
 
     private AlarmState _currentState = AlarmState.Normal;
     private readonly AlarmTriggerType _triggerType;
@@ -56,7 +58,8 @@ public class AlarmActor : ReceiveActor
         Script<object?>? onTriggerCompiledScript,
         SharedScriptLibrary sharedScriptLibrary,
         SiteRuntimeOptions options,
-        ILogger logger)
+        ILogger logger,
+        ISiteHealthCollector? healthCollector = null)
     {
         _alarmName = alarmName;
         _instanceName = instanceName;
@@ -64,6 +67,7 @@ public class AlarmActor : ReceiveActor
         _sharedScriptLibrary = sharedScriptLibrary;
         _options = options;
         _logger = logger;
+        _healthCollector = healthCollector;
         _priority = alarmConfig.PriorityLevel;
         _onTriggerScriptName = alarmConfig.OnTriggerScriptCanonicalName;
         _onTriggerCompiledScript = onTriggerCompiledScript;
@@ -164,6 +168,7 @@ public class AlarmActor : ReceiveActor
         }
         catch (Exception ex)
         {
+            _healthCollector?.IncrementAlarmError();
             // Alarm evaluation errors logged, actor continues
             _logger.LogError(ex,
                 "Alarm {Alarm} evaluation error on {Instance}",