fix(ui): templates root-menu Escape + double-menu guard + reorder disabled tests (#258)

- Root context menu now has tabindex/focus + Escape-key close (OnRootMenuKeyDown) mirroring the node menu
- Opening root menu calls _tree.DismissNodeContextMenu(); opening node menu fires OnNodeContextMenuOpened → DismissRootContextMenu so only one menu is ever visible
- Add FolderContextMenu_MoveUp_IsDisabled_OnFirstSibling and FolderContextMenu_MoveDown_IsDisabled_OnLastSibling bUnit tests

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Design/Templates.razor

@@ -81,7 +81,8 @@
                                 SelectionMode="TreeViewSelectionMode.Single"
                                 ExtraTemplateChildren="BuildCompositionLeavesFor"
                                 Filter="@_searchText"
-                                StorageKey="templates-tree">
+                                StorageKey="templates-tree"
+                                OnNodeContextMenuOpened="DismissRootContextMenu">
                 <NodeContent Context="node">
                     @RenderNodeLabel(node)
                 </NodeContent>
@@ -98,8 +99,10 @@
         {
             <div class="tv-ctx-overlay" @onclick="DismissRootContextMenu"
                  style="position:fixed;top:0;left:0;width:100vw;height:100vh;z-index:1049;background:transparent;"></div>
-            <div class="dropdown-menu show tv-root-menu" @onclick="DismissRootContextMenu"
-                 style="position:fixed;top:@(_rootMenuY)px;left:@(_rootMenuX)px;z-index:1050;">
+            <div class="dropdown-menu show tv-root-menu" tabindex="-1" @ref="_rootMenuRef"
+                 @onclick="DismissRootContextMenu"
+                 @onkeydown="OnRootMenuKeyDown"
+                 style="position:fixed;top:@(_rootMenuY)px;left:@(_rootMenuX)px;z-index:1050;outline:none;">
                 <button class="dropdown-item" @onclick="() => OpenNewFolderDialog(null)">New Folder</button>
                 <button class="dropdown-item" @onclick='() => NavigationManager.NavigateTo("/design/templates/create")'>New Template</button>
             </div>
@@ -415,16 +418,41 @@
     private bool _showRootMenu;
     private double _rootMenuX;
     private double _rootMenuY;
+    private bool _rootMenuNeedsFocus;
+    private ElementReference _rootMenuRef;
 
     private void OpenRootContextMenu(MouseEventArgs e)
     {
+        // Guard: dismiss any open node context menu first so both menus are
+        // never visible simultaneously (double-menu flash fix, #258).
+        _tree.DismissNodeContextMenu();
+
         _rootMenuX = e.ClientX;
         _rootMenuY = e.ClientY;
         _showRootMenu = true;
+        _rootMenuNeedsFocus = true;
     }
 
     private void DismissRootContextMenu() => _showRootMenu = false;
 
+    private void OnRootMenuKeyDown(KeyboardEventArgs e)
+    {
+        if (e.Key == "Escape")
+            DismissRootContextMenu();
+    }
+
+    protected override async Task OnAfterRenderAsync(bool firstRender)
+    {
+        if (_rootMenuNeedsFocus && _showRootMenu)
+        {
+            _rootMenuNeedsFocus = false;
+            try { await _rootMenuRef.FocusAsync(); }
+            catch (Microsoft.JSInterop.JSException) { }
+            catch (Microsoft.JSInterop.JSDisconnectedException) { }
+            catch (InvalidOperationException) { }
+        }
+    }
+
     // Rename folder dialog: opened via IDialogService.ShowAsync. The body seeds the
     // input from the current name and returns the trimmed new name on Save, or null on
     // Cancel; server guard failures surface via a toast.