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>

tests/ZB.MOM.WW.LmxOpcUa.Client.Shared.Tests/Fakes/FakeEndpointDiscovery.cs

@@ -0,0 +1,34 @@
+using Opc.Ua;
+using ZB.MOM.WW.LmxOpcUa.Client.Shared.Adapters;
+
+namespace ZB.MOM.WW.LmxOpcUa.Client.Shared.Tests.Fakes;
+
+internal sealed class FakeEndpointDiscovery : IEndpointDiscovery
+{
+    public bool ThrowOnSelect { get; set; }
+    public int SelectCallCount { get; private set; }
+    public string? LastEndpointUrl { get; private set; }
+
+    public EndpointDescription SelectEndpoint(ApplicationConfiguration config, string endpointUrl, MessageSecurityMode requestedMode)
+    {
+        SelectCallCount++;
+        LastEndpointUrl = endpointUrl;
+
+        if (ThrowOnSelect)
+            throw new InvalidOperationException($"No endpoint found for {endpointUrl}");
+
+        return new EndpointDescription
+        {
+            EndpointUrl = endpointUrl,
+            SecurityMode = requestedMode,
+            SecurityPolicyUri = requestedMode == MessageSecurityMode.None
+                ? SecurityPolicies.None
+                : SecurityPolicies.Basic256Sha256,
+            Server = new ApplicationDescription
+            {
+                ApplicationName = "FakeServer",
+                ApplicationUri = "urn:localhost:FakeServer"
+            }
+        };
+    }
+}