feat(uns): lazy per-equipment tag + virtual-tag load

Add LoadEquipmentChildrenAsync to IUnsTreeService and UnsTreeService; returns
Tag nodes (ordered by Name) then VirtualTag nodes (ordered by Name) as leaf
nodes with ChildCount=0, HasLazyChildren=false, keys tag:{id}/vtag:{id}.

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/IUnsTreeService.cs

@@ -4,7 +4,7 @@ namespace ZB.MOM.WW.OtOpcUa.AdminUI.Uns;
 /// Loads the structural portion of the unified-namespace (UNS) browse tree —
 /// Enterprise → Cluster → Area → Line → Equipment — from the config database.
 /// Equipment children (tags/virtual tags) are summarised by count only and loaded
-/// lazily by the renderer; this service never returns Tag/VirtualTag leaf nodes.
+/// lazily by the renderer via <see cref="LoadEquipmentChildrenAsync"/>.
 /// </summary>
 public interface IUnsTreeService
 {
@@ -16,4 +16,14 @@ public interface IUnsTreeService
     /// <param name="ct">A token to cancel the load.</param>
     /// <returns>The enterprise root nodes, each populated down to equipment.</returns>
     Task<IReadOnlyList<UnsNode>> LoadStructureAsync(CancellationToken ct = default);
+
+    /// <summary>
+    /// Lazily loads the Tag and VirtualTag leaf nodes for a single equipment node.
+    /// Tags are returned first (ordered by Name), followed by VirtualTags (ordered by Name).
+    /// Leaf nodes carry <c>ChildCount = 0</c> and <c>HasLazyChildren = false</c>.
+    /// </summary>
+    /// <param name="equipmentId">The equipment whose children to load.</param>
+    /// <param name="ct">A token to cancel the load.</param>
+    /// <returns>Tag nodes followed by VirtualTag nodes; empty if the equipment has none.</returns>
+    Task<IReadOnlyList<UnsNode>> LoadEquipmentChildrenAsync(string equipmentId, CancellationToken ct = default);
 }