fix(notification-outbox): re-align Central UI sandbox Notify API with production

The script-analysis sandbox Notify surface was stale after the Notification
Outbox change: SandboxNotifyTarget.Send returned Task<NotificationResult> and
there was no Status method, while production NotifyTarget.Send returns
Task<string> (a NotificationId) plus NotifyHelper.Status. A script that
test-ran cleanly in the sandbox would not compile against the real site
runtime.

- Move the NotificationDeliveryStatus record from ScadaLink.SiteRuntime.Scripts
  into ScadaLink.Commons.Messages.Notification so both production and the
  CentralUI sandbox reference the exact same type (CentralUI does not, and
  should not, reference SiteRuntime). Production NotifyHelper.Status is
  otherwise untouched.
- Rewrite SandboxNotifyHelper/SandboxNotifyTarget to be a signature-faithful
  no-op fake: Send returns Task<string> (a fake NotificationId), Status returns
  Task<NotificationDeliveryStatus>. Production now enqueues into the site S&F
  engine, which has no central-side equivalent in the sandbox, so the fake no
  longer carries an INotificationDeliveryService.
- Add script-analysis tests proving a script using the new Notify shape both
  diagnoses clean and runs in the sandbox.

src/ScadaLink.Commons/Messages/Notification/NotificationMessages.cs

@@ -40,3 +40,18 @@ public record NotificationStatusResponse(
     int RetryCount,
     string? LastError,
     DateTimeOffset? DeliveredAt);
+
+/// <summary>
+/// Notification Outbox: the delivery status of a notification, as returned to a
+/// script by <c>Notify.Status(id)</c>.
+///
+/// <see cref="Status"/> is either a central status (<c>Pending</c>, <c>Retrying</c>,
+/// <c>Delivered</c>, <c>Parked</c>, <c>Discarded</c>), the site-local <c>Forwarding</c>
+/// state (the notification is still buffered at the site and has not yet been
+/// forwarded/acked), or <c>Unknown</c> (no central row and not buffered locally).
+/// </summary>
+public record NotificationDeliveryStatus(
+    string Status,
+    int RetryCount,
+    string? LastError,
+    DateTimeOffset? DeliveredAt);