Add cross-platform OPC UA client stack: shared library, CLI tool, and Avalonia UI

Implements Client.Shared (IOpcUaClientService with connection lifecycle, failover,
browse, read/write, subscriptions, alarms, history, redundancy), Client.CLI (8 CliFx
commands mirroring tools/opcuacli-dotnet), and Client.UI (Avalonia desktop app with
tree browser, read/write, subscriptions, alarms, and history tabs). All three target
.NET 10 and are covered by 249 unit tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.LmxOpcUa.Client.UI/Views/MainWindow.axaml.cs

@@ -0,0 +1,34 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using ZB.MOM.WW.LmxOpcUa.Client.UI.ViewModels;
+
+namespace ZB.MOM.WW.LmxOpcUa.Client.UI.Views;
+
+public partial class MainWindow : Window
+{
+    public MainWindow()
+    {
+        InitializeComponent();
+    }
+
+    protected override void OnLoaded(RoutedEventArgs e)
+    {
+        base.OnLoaded(e);
+
+        // Wire up tree selection to the main ViewModel
+        var browseTreeView = this.FindControl<BrowseTreeView>("BrowseTreePanel");
+        var treeView = browseTreeView?.FindControl<TreeView>("BrowseTree");
+        if (treeView != null)
+        {
+            treeView.SelectionChanged += OnTreeSelectionChanged;
+        }
+    }
+
+    private void OnTreeSelectionChanged(object? sender, SelectionChangedEventArgs e)
+    {
+        if (DataContext is MainWindowViewModel vm && sender is TreeView treeView)
+        {
+            vm.SelectedTreeNode = treeView.SelectedItem as TreeNodeViewModel;
+        }
+    }
+}