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/Status/HealthCheckService.cs

@@ -0,0 +1,57 @@
+using ZB.MOM.WW.LmxOpcUa.Host.Domain;
+using ZB.MOM.WW.LmxOpcUa.Host.Metrics;
+
+namespace ZB.MOM.WW.LmxOpcUa.Host.Status
+{
+    /// <summary>
+    /// Determines health status based on connection state and operation success rates. (DASH-003)
+    /// </summary>
+    public class HealthCheckService
+    {
+        public HealthInfo CheckHealth(ConnectionState connectionState, PerformanceMetrics? metrics)
+        {
+            // Rule 1: Not connected → Unhealthy
+            if (connectionState != ConnectionState.Connected)
+            {
+                return new HealthInfo
+                {
+                    Status = "Unhealthy",
+                    Message = $"MXAccess not connected (state: {connectionState})",
+                    Color = "red"
+                };
+            }
+
+            // Rule 2: Success rate < 50% with > 100 ops → Degraded
+            if (metrics != null)
+            {
+                var stats = metrics.GetStatistics();
+                foreach (var kvp in stats)
+                {
+                    if (kvp.Value.TotalCount > 100 && kvp.Value.SuccessRate < 0.5)
+                    {
+                        return new HealthInfo
+                        {
+                            Status = "Degraded",
+                            Message = $"{kvp.Key} success rate is {kvp.Value.SuccessRate:P0} ({kvp.Value.TotalCount} ops)",
+                            Color = "yellow"
+                        };
+                    }
+                }
+            }
+
+            // Rule 3: All good
+            return new HealthInfo
+            {
+                Status = "Healthy",
+                Message = "All systems operational",
+                Color = "green"
+            };
+        }
+
+        public bool IsHealthy(ConnectionState connectionState, PerformanceMetrics? metrics)
+        {
+            var health = CheckHealth(connectionState, metrics);
+            return health.Status != "Unhealthy";
+        }
+    }
+}