feat: thread BrowseNext continuation token through actor + BrowseService (T15)

src/ZB.MOM.WW.ScadaBridge.CentralUI/Services/IBrowseService.cs

@@ -28,11 +28,13 @@ public interface IBrowseService
     /// <param name="siteId">The target site identifier.</param>
     /// <param name="connectionName">Name of the site-local data connection to browse against — the site's <c>DataConnectionManagerActor</c> indexes its children by name.</param>
     /// <param name="parentNodeId">Node to browse, or <c>null</c> to browse from the server root.</param>
+    /// <param name="continuationToken">Opaque cursor from a prior <see cref="BrowseNodeResult.ContinuationToken"/> to fetch the NEXT page under <paramref name="parentNodeId"/>; <c>null</c> for the first page.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
     /// <returns>A task that resolves to a <see cref="BrowseNodeResult"/> containing child nodes or a <see cref="BrowseFailure"/> on error.</returns>
     Task<BrowseNodeResult> BrowseChildrenAsync(
         string siteId,
         string connectionName,
         string? parentNodeId,
+        string? continuationToken = null,
         CancellationToken cancellationToken = default);
 }