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/ViewModels/SubscriptionItemViewModel.cs

@@ -0,0 +1,30 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace ZB.MOM.WW.LmxOpcUa.Client.UI.ViewModels;
+
+/// <summary>
+/// Represents a single active subscription row.
+/// </summary>
+public partial class SubscriptionItemViewModel : ObservableObject
+{
+    /// <summary>The monitored NodeId.</summary>
+    public string NodeId { get; }
+
+    /// <summary>The subscription interval in milliseconds.</summary>
+    public int IntervalMs { get; }
+
+    [ObservableProperty]
+    private string? _value;
+
+    [ObservableProperty]
+    private string? _status;
+
+    [ObservableProperty]
+    private string? _timestamp;
+
+    public SubscriptionItemViewModel(string nodeId, int intervalMs)
+    {
+        NodeId = nodeId;
+        IntervalMs = intervalMs;
+    }
+}