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.SiteRuntime/Scripts/ScriptCompilationService.cs

@@ -178,4 +178,28 @@ public class ScriptGlobals
     public IReadOnlyDictionary<string, object?> Parameters { get; set; } =
         new Dictionary<string, object?>();
     public CancellationToken CancellationToken { get; set; }
+
+    /// <summary>
+    /// Top-level ExternalSystem access for scripts (delegates to Instance.ExternalSystem).
+    /// Usage: ExternalSystem.Call("systemName", "methodName", params)
+    /// </summary>
+    public ScriptRuntimeContext.ExternalSystemHelper ExternalSystem => Instance.ExternalSystem;
+
+    /// <summary>
+    /// Top-level Database access for scripts (delegates to Instance.Database).
+    /// Usage: Database.Connection("name") or Database.CachedWrite("name", "sql", params)
+    /// </summary>
+    public ScriptRuntimeContext.DatabaseHelper Database => Instance.Database;
+
+    /// <summary>
+    /// Top-level Notify access for scripts (delegates to Instance.Notify).
+    /// Usage: Notify.To("listName").Send("subject", "message")
+    /// </summary>
+    public ScriptRuntimeContext.NotifyHelper Notify => Instance.Notify;
+
+    /// <summary>
+    /// Top-level Scripts access for shared script calls (delegates to Instance.Scripts).
+    /// Usage: Scripts.CallShared("scriptName", params)
+    /// </summary>
+    public ScriptRuntimeContext.ScriptCallHelper Scripts => Instance.Scripts;
 }