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/GalaxyRepository/ChangeDetectionService.cs

@@ -0,0 +1,96 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Serilog;
+using ZB.MOM.WW.LmxOpcUa.Host.Configuration;
+using ZB.MOM.WW.LmxOpcUa.Host.Domain;
+
+namespace ZB.MOM.WW.LmxOpcUa.Host.GalaxyRepository
+{
+    /// <summary>
+    /// Polls the Galaxy database for deployment changes and fires OnGalaxyChanged. (GR-003, GR-004)
+    /// </summary>
+    public class ChangeDetectionService : IDisposable
+    {
+        private static readonly ILogger Log = Serilog.Log.ForContext<ChangeDetectionService>();
+
+        private readonly IGalaxyRepository _repository;
+        private readonly int _intervalSeconds;
+        private CancellationTokenSource? _cts;
+        private DateTime? _lastKnownDeployTime;
+
+        public event Action? OnGalaxyChanged;
+        public DateTime? LastKnownDeployTime => _lastKnownDeployTime;
+
+        public ChangeDetectionService(IGalaxyRepository repository, int intervalSeconds)
+        {
+            _repository = repository;
+            _intervalSeconds = intervalSeconds;
+        }
+
+        public void Start()
+        {
+            _cts = new CancellationTokenSource();
+            Task.Run(() => PollLoopAsync(_cts.Token));
+            Log.Information("Change detection started (interval={Interval}s)", _intervalSeconds);
+        }
+
+        public void Stop()
+        {
+            _cts?.Cancel();
+            Log.Information("Change detection stopped");
+        }
+
+        private async Task PollLoopAsync(CancellationToken ct)
+        {
+            // First poll always triggers
+            bool firstPoll = true;
+
+            while (!ct.IsCancellationRequested)
+            {
+                try
+                {
+                    var deployTime = await _repository.GetLastDeployTimeAsync(ct);
+
+                    if (firstPoll)
+                    {
+                        firstPoll = false;
+                        _lastKnownDeployTime = deployTime;
+                        Log.Information("Initial deploy time: {DeployTime}", deployTime);
+                        OnGalaxyChanged?.Invoke();
+                    }
+                    else if (deployTime != _lastKnownDeployTime)
+                    {
+                        Log.Information("Galaxy deployment change detected: {Previous} → {Current}",
+                            _lastKnownDeployTime, deployTime);
+                        _lastKnownDeployTime = deployTime;
+                        OnGalaxyChanged?.Invoke();
+                    }
+                }
+                catch (OperationCanceledException)
+                {
+                    break;
+                }
+                catch (Exception ex)
+                {
+                    Log.Warning(ex, "Change detection poll failed, will retry next interval");
+                }
+
+                try
+                {
+                    await Task.Delay(TimeSpan.FromSeconds(_intervalSeconds), ct);
+                }
+                catch (OperationCanceledException)
+                {
+                    break;
+                }
+            }
+        }
+
+        public void Dispose()
+        {
+            Stop();
+            _cts?.Dispose();
+        }
+    }
+}