fix: handle threading issues for concurrent clients joining

src/PepperDash.Essentials.MobileControl/WebSocketServer/UiClient.cs

@@ -31,6 +31,11 @@ namespace PepperDash.Essentials.WebSocketServer
         /// </summary>
         public string Token { get; private set; }
 
+        /// <summary>
+        /// The URL token key used to connect (from UiClientContexts dictionary key)
+        /// </summary>
+        public string TokenKey { get; set; }
+
         /// <summary>
         /// Touchpanel Key associated with this client
         /// </summary>