fix: wire up health report pipeline between sites and central aggregator

Sites now send SiteHealthReport via AkkaHealthReportTransport →
SiteCommunicationActor → CentralCommunicationActor → CentralHealthAggregator.
Added IHealthReportTransport impl, ISiteIdentityProvider impl, registered
HealthReportSender on site nodes, and added SiteHealthReport handler in
CentralCommunicationActor. Health Dashboard now shows all 3 sites online.

src/ScadaLink.Communication/Actors/CentralCommunicationActor.cs

@@ -4,6 +4,7 @@ using Microsoft.Extensions.DependencyInjection;
 using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Messages.Communication;
 using ScadaLink.Commons.Messages.Health;
+using ScadaLink.HealthMonitoring;
 
 namespace ScadaLink.Communication.Actors;
 
@@ -50,8 +51,9 @@ public class CentralCommunicationActor : ReceiveActor
         // Periodic refresh trigger
         Receive<RefreshSiteAddresses>(_ => LoadSiteAddressesFromDb());
 
-        // Site registration via heartbeats
+        // Health monitoring: heartbeats and health reports from sites
         Receive<HeartbeatMessage>(HandleHeartbeat);
+        Receive<SiteHealthReport>(HandleSiteHealthReport);
 
         // Connection state changes
         Receive<ConnectionStateChanged>(HandleConnectionStateChanged);
@@ -62,10 +64,23 @@ public class CentralCommunicationActor : ReceiveActor
 
     private void HandleHeartbeat(HeartbeatMessage heartbeat)
     {
-        // Forward heartbeat to parent/subscribers (central health monitoring)
+        // Forward heartbeat to parent for any interested central actors
         Context.Parent.Tell(heartbeat);
     }
 
+    private void HandleSiteHealthReport(SiteHealthReport report)
+    {
+        var aggregator = _serviceProvider.GetService<ICentralHealthAggregator>();
+        if (aggregator != null)
+        {
+            aggregator.ProcessReport(report);
+        }
+        else
+        {
+            _log.Warning("ICentralHealthAggregator not available, dropping health report from site {0}", report.SiteId);
+        }
+    }
+
     private void HandleConnectionStateChanged(ConnectionStateChanged msg)
     {
         if (!msg.IsConnected)

src/ScadaLink.Communication/ScadaLink.Communication.csproj

@@ -20,6 +20,7 @@
 
   <ItemGroup>
     <ProjectReference Include="../ScadaLink.Commons/ScadaLink.Commons.csproj" />
+    <ProjectReference Include="../ScadaLink.HealthMonitoring/ScadaLink.HealthMonitoring.csproj" />
   </ItemGroup>
 
 </Project>

src/ScadaLink.Host/AkkaHealthReportTransport.cs

@@ -0,0 +1,29 @@
+using Akka.Actor;
+using ScadaLink.Commons.Messages.Health;
+using ScadaLink.HealthMonitoring;
+using ScadaLink.Host.Actors;
+
+namespace ScadaLink.Host;
+
+/// <summary>
+/// Sends SiteHealthReport to the local SiteCommunicationActor via Akka ActorSelection.
+/// The SiteCommunicationActor forwards it to central.
+/// </summary>
+public class AkkaHealthReportTransport : IHealthReportTransport
+{
+    private readonly AkkaHostedService _akkaService;
+
+    public AkkaHealthReportTransport(AkkaHostedService akkaService)
+    {
+        _akkaService = akkaService;
+    }
+
+    public void Send(SiteHealthReport report)
+    {
+        var actorSystem = _akkaService.ActorSystem;
+        if (actorSystem == null) return;
+
+        var siteComm = actorSystem.ActorSelection("/user/site-communication");
+        siteComm.Tell(report, ActorRefs.NoSender);
+    }
+}

src/ScadaLink.Host/Program.cs

@@ -151,10 +151,14 @@ try
             // Shared components
             services.AddClusterInfrastructure();
             services.AddCommunication();
-            services.AddHealthMonitoring();
+            services.AddSiteHealthMonitoring();
             services.AddExternalSystemGateway();
             services.AddNotificationService();
 
+            // Health report transport: sends SiteHealthReport to SiteCommunicationActor via Akka
+            services.AddSingleton<ISiteIdentityProvider, SiteIdentityProvider>();
+            services.AddSingleton<IHealthReportTransport, AkkaHealthReportTransport>();
+
             // Site-only components — AddSiteRuntime registers SiteStorageService with SQLite path
             // and site-local repository implementations (IExternalSystemRepository, INotificationRepository)
             var siteDbPath = context.Configuration["ScadaLink:Database:SiteDbPath"] ?? "site.db";

src/ScadaLink.Host/SiteIdentityProvider.cs

@@ -0,0 +1,18 @@
+using Microsoft.Extensions.Options;
+using ScadaLink.HealthMonitoring;
+
+namespace ScadaLink.Host;
+
+/// <summary>
+/// Provides the site identity from NodeOptions configuration.
+/// </summary>
+public class SiteIdentityProvider : ISiteIdentityProvider
+{
+    public string SiteId { get; }
+
+    public SiteIdentityProvider(IOptions<NodeOptions> nodeOptions)
+    {
+        SiteId = nodeOptions.Value.SiteId
+            ?? throw new InvalidOperationException("SiteId is required for site nodes.");
+    }
+}