feat(lmxproxy): phase 2 — host core (MxAccessClient, SessionManager, SubscriptionManager)

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

lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/Domain/SubscriptionStats.cs

@@ -0,0 +1,17 @@
+namespace ZB.MOM.WW.LmxProxy.Host.Domain
+{
+    /// <summary>Subscription statistics for monitoring.</summary>
+    public class SubscriptionStats
+    {
+        public SubscriptionStats(int totalClients, int totalTags, int activeSubscriptions)
+        {
+            TotalClients = totalClients;
+            TotalTags = totalTags;
+            ActiveSubscriptions = activeSubscriptions;
+        }
+
+        public int TotalClients { get; }
+        public int TotalTags { get; }
+        public int ActiveSubscriptions { get; }
+    }
+}