feat: wire ExternalSystem, Database, and Notify APIs into script runtime

IServiceProvider now flows through the actor chain (DeploymentManagerActor
→ InstanceActor → ScriptActor → ScriptExecutionActor) so scripts can
resolve IExternalSystemClient, IDatabaseGateway, and
INotificationDeliveryService from DI. ScriptGlobals exposes ExternalSystem,
Database, Notify, and Scripts as top-level properties so scripts can use
them without the Instance. prefix.

src/ScadaLink.Host/SiteServiceRegistration.cs

@@ -0,0 +1,63 @@
+using ScadaLink.ClusterInfrastructure;
+using ScadaLink.Communication;
+using ScadaLink.DataConnectionLayer;
+using ScadaLink.ExternalSystemGateway;
+using ScadaLink.HealthMonitoring;
+using ScadaLink.Host.Actors;
+using ScadaLink.NotificationService;
+using ScadaLink.SiteEventLogging;
+using ScadaLink.SiteRuntime;
+using ScadaLink.StoreAndForward;
+
+namespace ScadaLink.Host;
+
+/// <summary>
+/// Extracted site-role DI registrations so both Program.cs and tests
+/// use the same composition root.
+/// </summary>
+public static class SiteServiceRegistration
+{
+    public static void Configure(IServiceCollection services, IConfiguration config)
+    {
+        // Shared components
+        services.AddClusterInfrastructure();
+        services.AddCommunication();
+        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 = config["ScadaLink:Database:SiteDbPath"] ?? "site.db";
+        services.AddSiteRuntime($"Data Source={siteDbPath}");
+        services.AddDataConnectionLayer();
+        services.AddStoreAndForward();
+        services.AddSiteEventLogging();
+
+        // WP-13: Akka.NET bootstrap via hosted service
+        services.AddSingleton<AkkaHostedService>();
+        services.AddHostedService(sp => sp.GetRequiredService<AkkaHostedService>());
+
+        // Options binding
+        BindSharedOptions(services, config);
+        services.Configure<SiteRuntimeOptions>(config.GetSection("ScadaLink:SiteRuntime"));
+        services.Configure<DataConnectionOptions>(config.GetSection("ScadaLink:DataConnection"));
+        services.Configure<StoreAndForwardOptions>(config.GetSection("ScadaLink:StoreAndForward"));
+        services.Configure<SiteEventLogOptions>(config.GetSection("ScadaLink:SiteEventLog"));
+    }
+
+    public static void BindSharedOptions(IServiceCollection services, IConfiguration config)
+    {
+        services.Configure<NodeOptions>(config.GetSection("ScadaLink:Node"));
+        services.Configure<ClusterOptions>(config.GetSection("ScadaLink:Cluster"));
+        services.Configure<DatabaseOptions>(config.GetSection("ScadaLink:Database"));
+        services.Configure<CommunicationOptions>(config.GetSection("ScadaLink:Communication"));
+        services.Configure<HealthMonitoringOptions>(config.GetSection("ScadaLink:HealthMonitoring"));
+        services.Configure<NotificationOptions>(config.GetSection("ScadaLink:Notification"));
+        services.Configure<LoggingOptions>(config.GetSection("ScadaLink:Logging"));
+    }
+}