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/ScriptActor.cs

@@ -4,6 +4,7 @@ using Microsoft.Extensions.Logging;
 using ScadaLink.Commons.Messages.ScriptExecution;
 using ScadaLink.Commons.Messages.Streaming;
 using ScadaLink.Commons.Types.Flattening;
+using ScadaLink.HealthMonitoring;
 using ScadaLink.SiteRuntime.Scripts;
 using System.Text.Json;
 
@@ -29,6 +30,7 @@ public class ScriptActor : ReceiveActor, IWithTimers
     private readonly SharedScriptLibrary _sharedScriptLibrary;
     private readonly SiteRuntimeOptions _options;
     private readonly ILogger _logger;
+    private readonly ISiteHealthCollector? _healthCollector;
 
     private Script<object?>? _compiledScript;
     private ScriptTriggerConfig? _triggerConfig;
@@ -46,7 +48,8 @@ public class ScriptActor : ReceiveActor, IWithTimers
         ResolvedScript scriptConfig,
         SharedScriptLibrary sharedScriptLibrary,
         SiteRuntimeOptions options,
-        ILogger logger)
+        ILogger logger,
+        ISiteHealthCollector? healthCollector = null)
     {
         _scriptName = scriptName;
         _instanceName = instanceName;
@@ -55,6 +58,7 @@ public class ScriptActor : ReceiveActor, IWithTimers
         _sharedScriptLibrary = sharedScriptLibrary;
         _options = options;
         _logger = logger;
+        _healthCollector = healthCollector;
         _minTimeBetweenRuns = scriptConfig.MinTimeBetweenRuns;
 
         // Parse trigger configuration
@@ -207,7 +211,8 @@ public class ScriptActor : ReceiveActor, IWithTimers
             _options,
             replyTo,
             correlationId,
-            _logger));
+            _logger,
+            _healthCollector));
 
         Context.ActorOf(props, executionId);
     }