Implement LmxOpcUa server — all 6 phases complete

Full OPC UA server on .NET Framework 4.8 (x86) exposing AVEVA System
Platform Galaxy tags via MXAccess. Mirrors Galaxy object hierarchy as
OPC UA address space, translating contained-name browse paths to
tag-name runtime references.

Components implemented:
- Configuration: AppConfiguration with 4 sections, validator
- Domain: ConnectionState, Quality, Vtq, MxDataTypeMapper, error codes
- MxAccess: StaComThread, MxAccessClient (partial classes), MxProxyAdapter
  using strongly-typed ArchestrA.MxAccess COM interop
- Galaxy Repository: SQL queries (hierarchy, attributes, change detection),
  ChangeDetectionService with auto-rebuild on deploy
- OPC UA Server: LmxNodeManager (CustomNodeManager2), LmxOpcUaServer,
  OpcUaServerHost with programmatic config, SecurityPolicy None
- Status Dashboard: HTTP server with HTML/JSON/health endpoints
- Integration: Full 14-step startup, graceful shutdown, component wiring

175 tests (174 unit + 1 integration), all passing.

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

src/ZB.MOM.WW.LmxOpcUa.Host/Domain/ConnectionStateChangedEventArgs.cs

@@ -0,0 +1,21 @@
+using System;
+
+namespace ZB.MOM.WW.LmxOpcUa.Host.Domain
+{
+    /// <summary>
+    /// Event args for connection state transitions. (MXA-002)
+    /// </summary>
+    public class ConnectionStateChangedEventArgs : EventArgs
+    {
+        public ConnectionState PreviousState { get; }
+        public ConnectionState CurrentState { get; }
+        public string Message { get; }
+
+        public ConnectionStateChangedEventArgs(ConnectionState previous, ConnectionState current, string message = "")
+        {
+            PreviousState = previous;
+            CurrentState = current;
+            Message = message ?? "";
+        }
+    }
+}