feat(notif-outbox): carry + persist SourceNode end-to-end via NotificationSubmit

Site: inject INodeIdentityProvider where NotificationSubmit is built; stamp
SourceNode = NodeName at construction.

Central: NotificationOutboxActor.HandleSubmit copies submit.SourceNode onto
the Notification row; the repository INSERT persists it (EF tracked-entity
insert flows it through automatically; raw-SQL extension if not).

After this commit, every Notifications row carries the originating site
node-a/node-b in SourceNode. Existing notifications submitted pre-feature
remain NULL.

src/ScadaLink.SiteRuntime/Actors/ScriptExecutionActor.cs

@@ -124,6 +124,13 @@ public class ScriptExecutionActor : ReceiveActor
                 // to the no-emission path (the underlying S&F handoff still
                 // happens and a TrackedOperationId is still returned).
                 ICachedCallTelemetryForwarder? cachedForwarder = null;
+                // SourceNode-stamping (Tasks 13/14): the local node name
+                // resolved from INodeIdentityProvider — node-a/node-b on site
+                // hosts. Null in tests / hosts that haven't registered the
+                // provider, in which case NotificationSubmit.SourceNode and
+                // SiteCallOperational.SourceNode stay null and central
+                // persists the rows with SourceNode NULL.
+                string? sourceNode = null;
 
                 if (serviceProvider != null)
                 {
@@ -136,6 +143,7 @@ public class ScriptExecutionActor : ReceiveActor
                     auditWriter = serviceScope.ServiceProvider.GetService<IAuditWriter>();
                     operationTrackingStore = serviceScope.ServiceProvider.GetService<IOperationTrackingStore>();
                     cachedForwarder = serviceScope.ServiceProvider.GetService<ICachedCallTelemetryForwarder>();
+                    sourceNode = serviceScope.ServiceProvider.GetService<INodeIdentityProvider>()?.NodeName;
                 }
 
                 var context = new ScriptRuntimeContext(
@@ -175,7 +183,13 @@ public class ScriptExecutionActor : ReceiveActor
                     // id for an inbound-API-routed call. The routed script still
                     // mints its own fresh ExecutionId — this records the spawner.
                     // Null for normal (tag-change / timer) runs.
-                    parentExecutionId: parentExecutionId);
+                    parentExecutionId: parentExecutionId,
+                    // SourceNode-stamping (Tasks 13/14): the local node name
+                    // (node-a/node-b on a site) — threaded down so Notify.Send
+                    // and the four cached-call telemetry constructors can stamp
+                    // it onto NotificationSubmit.SourceNode and
+                    // SiteCallOperational.SourceNode respectively.
+                    sourceNode: sourceNode);
 
                 var globals = new ScriptGlobals
                 {