fix(uns): bind _filter + modal parent-ids as Razor expressions, not literals

GlobalUns passed string component params without an @ prefix
(Filter="_filter", ClusterId="_areaModalClusterId", etc.). Razor treats a
string-typed component-parameter value without @ as a LITERAL, so UnsTree.Filter
became the literal "_filter" and the modals received literal field-name strings
as their parent ids. The non-empty literal filter matched no node, so the tree
never rendered children beyond the enterprise roots; the modals would have created
children under a bogus cluster/area/line/equipment id.

Add @ to the six string-param bindings. Verified live in docker-dev: the full
Enterprise->Cluster->Area->Line->Equipment tree renders and an area created via the
modal persists with the correct ClusterId (MAIN). No unit test added — this is a
Razor binding issue not reachable without bUnit (not used in this project).

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Pages/Uns/GlobalUns.razor

@@ -38,7 +38,7 @@
     else
     {
         <div style="padding:.5rem 1rem">
-            <UnsTree Roots="_roots" Filter="_filter"
+            <UnsTree Roots="_roots" Filter="@_filter"
                      OnToggleExpand="ToggleAsync"
                      OnAddChild="HandleAddChild"
                      OnAddVirtualTag="HandleAddVirtualTag"
@@ -50,7 +50,7 @@
 
 <AreaModal Visible="_areaModalVisible"
            IsNew="_areaModalIsNew"
-           ClusterId="_areaModalClusterId"
+           ClusterId="@_areaModalClusterId"
            Existing="_areaModalExisting"
            Clusters="ClusterOptions"
            OnSaved="OnModalSavedAsync"
@@ -58,7 +58,7 @@
 
 <LineModal Visible="_lineModalVisible"
            IsNew="_lineModalIsNew"
-           UnsAreaId="_lineModalAreaId"
+           UnsAreaId="@_lineModalAreaId"
            Existing="_lineModalExisting"
            Areas="_lineModalAreaOptions"
            OnSaved="OnModalSavedAsync"
@@ -66,7 +66,7 @@
 
 <EquipmentModal Visible="_equipmentModalVisible"
                 IsNew="_equipmentModalIsNew"
-                UnsLineId="_equipmentModalLineId"
+                UnsLineId="@_equipmentModalLineId"
                 Existing="_equipmentModalExisting"
                 Lines="_equipmentModalLineOptions"
                 Drivers="_equipmentModalDriverOptions"
@@ -75,7 +75,7 @@
 
 <TagModal Visible="_tagModalVisible"
           IsNew="_tagModalIsNew"
-          EquipmentId="_tagModalEquipmentId"
+          EquipmentId="@_tagModalEquipmentId"
           Existing="_tagModalExisting"
           Drivers="_tagModalDriverOptions"
           OnSaved="OnEquipmentChildModalSavedAsync"
@@ -83,7 +83,7 @@
 
 <VirtualTagModal Visible="_vtagModalVisible"
                  IsNew="_vtagModalIsNew"
-                 EquipmentId="_vtagModalEquipmentId"
+                 EquipmentId="@_vtagModalEquipmentId"
                  Existing="_vtagModalExisting"
                  Scripts="_vtagModalScriptOptions"
                  OnSaved="OnEquipmentChildModalSavedAsync"