feat(mobile-control): track and validate UI client app versions

Extend the /system/clientJoined handler to accept an optional
`appVersion` field reported by connecting UI clients (e.g. the
React app's build-time APP_VERSION), so Essentials can record and
validate what's actually running against the configured
versions.touchpanelWrapperApp version.

- Add ConnectedClientVersionInfo to capture clientId, roomKey,
  touchpanelKey, reported/expected app version, and last-seen time.
- Add MobileControlSystemController.TrackClientAppVersion(), storing
  results in a new thread-safe ConnectedClientVersions dictionary and
  logging a warning on version mismatch.
- Expose ConnectedClientVersions as a public read-only property for
  diagnostics.
- Surface reported vs. expected versions per client in the
  `mobileinfo` console command output.

No wire protocol changes required; content is passed as-is over the
existing clientJoined message.

src/PepperDash.Essentials.MobileControl/ConnectedClientVersionInfo.cs

@@ -0,0 +1,47 @@
+using System;
+using Newtonsoft.Json;
+
+namespace PepperDash.Essentials
+{
+    /// <summary>
+    /// Represents the version information reported by a connected Mobile Control UI client
+    /// </summary>
+    public class ConnectedClientVersionInfo
+    {
+        /// <summary>
+        /// Gets or sets the client id
+        /// </summary>
+        [JsonProperty("clientId")]
+        public string ClientId { get; set; }
+
+        /// <summary>
+        /// Gets or sets the room key the client joined
+        /// </summary>
+        [JsonProperty("roomKey")]
+        public string RoomKey { get; set; }
+
+        /// <summary>
+        /// Gets or sets the touchpanel key the client joined as, if any
+        /// </summary>
+        [JsonProperty("touchpanelKey")]
+        public string TouchpanelKey { get; set; }
+
+        /// <summary>
+        /// Gets or sets the app version reported by the client (e.g. the React app's build-time APP_VERSION)
+        /// </summary>
+        [JsonProperty("appVersion")]
+        public string AppVersion { get; set; }
+
+        /// <summary>
+        /// Gets or sets the expected app version from the system config's versions.touchpanelWrapperApp, if configured
+        /// </summary>
+        [JsonProperty("expectedAppVersion")]
+        public string ExpectedAppVersion { get; set; }
+
+        /// <summary>
+        /// Gets or sets the UTC time the client last reported this version
+        /// </summary>
+        [JsonProperty("lastSeen")]
+        public DateTime LastSeen { get; set; }
+    }
+}

src/PepperDash.Essentials.MobileControl/MobileControlSystemController.cs

@@ -69,11 +69,32 @@ namespace PepperDash.Essentials
         private readonly Dictionary<string, IMobileControlMessenger> _defaultMessengers =
             new Dictionary<string, IMobileControlMessenger>();
 
+        private readonly Dictionary<string, ConnectedClientVersionInfo> _connectedClientVersions =
+            new Dictionary<string, ConnectedClientVersionInfo>(StringComparer.InvariantCultureIgnoreCase);
+
+        private readonly object _connectedClientVersionsLock = new object();
+
         /// <summary>
         /// Get the custom messengers with subscriptions
         /// </summary>
         public ReadOnlyDictionary<string, IMobileControlMessengerWithSubscriptions> Messengers => new ReadOnlyDictionary<string, IMobileControlMessengerWithSubscriptions>(_messengers.Values.OfType<IMobileControlMessengerWithSubscriptions>().ToDictionary(k => k.Key, v => v));
 
+        /// <summary>
+        /// Gets the most recently reported UI app version for each connected client, keyed by clientId
+        /// </summary>
+        public ReadOnlyDictionary<string, ConnectedClientVersionInfo> ConnectedClientVersions
+        {
+            get
+            {
+                lock (_connectedClientVersionsLock)
+                {
+                    return new ReadOnlyDictionary<string, ConnectedClientVersionInfo>(
+                        new Dictionary<string, ConnectedClientVersionInfo>(_connectedClientVersions)
+                    );
+                }
+            }
+        }
+
         /// <summary>
         /// Get the default messengers
         /// </summary>
@@ -1782,6 +1803,28 @@ namespace PepperDash.Essentials
                     "    Not Enabled in Config.\r\n"
                 );
             }
+
+            var connectedClientVersions = ConnectedClientVersions;
+
+            if (connectedClientVersions.Count == 0)
+            {
+                CrestronConsole.ConsoleCommandResponse("\r\nUI Client App Versions: None reported yet\r\n");
+            }
+            else
+            {
+                CrestronConsole.ConsoleCommandResponse("\r\nUI Client App Versions:\r\n");
+                foreach (var kv in connectedClientVersions)
+                {
+                    var v = kv.Value;
+                    var match = string.IsNullOrEmpty(v.ExpectedAppVersion) || string.Equals(v.ExpectedAppVersion, v.AppVersion, StringComparison.OrdinalIgnoreCase);
+
+                    CrestronConsole.ConsoleCommandResponse(
+                        $"  Client: {v.ClientId}  Touchpanel: {v.TouchpanelKey}  Room: {v.RoomKey}\r\n" +
+                        $"    Reported: {v.AppVersion}  Expected: {v.ExpectedAppVersion ?? "(not configured)"}  Match: {(match ? "Yes" : "NO - MISMATCH")}\r\n" +
+                        $"    Last Seen (UTC): {v.LastSeen:yyyy-MM-dd HH:mm:ss}\r\n"
+                    );
+                }
+            }
         }
 
         /// <summary>
@@ -2181,6 +2224,8 @@ namespace PepperDash.Essentials
             var roomKey = content["roomKey"].Value<string>();
             var touchpanelKey = content.SelectToken("touchpanelKey");
 
+            TrackClientAppVersion(clientId, roomKey, touchpanelKey?.Value<string>(), content.SelectToken("appVersion")?.Value<string>());
+
             if (_roomCombiner == null)
             {
                 var message = new MobileControlMessage
@@ -2252,6 +2297,50 @@ namespace PepperDash.Essentials
             SendTouchpanelKey(clientId, touchpanelKey);
         }
 
+        /// <summary>
+        /// Records the app version reported by a connecting UI client (e.g. the mobile control React app's
+        /// build-time APP_VERSION) and compares it against the configured versions.touchpanelWrapperApp version.
+        /// </summary>
+        private void TrackClientAppVersion(string clientId, string roomKey, string touchpanelKey, string appVersion)
+        {
+            if (string.IsNullOrEmpty(appVersion))
+            {
+                return;
+            }
+
+            var expectedVersion = ConfigReader.ConfigObject?.Versions?.TouchpanelWrapperApp?.Version;
+
+            var info = new ConnectedClientVersionInfo
+            {
+                ClientId = clientId,
+                RoomKey = roomKey,
+                TouchpanelKey = touchpanelKey,
+                AppVersion = appVersion,
+                ExpectedAppVersion = expectedVersion,
+                LastSeen = DateTime.UtcNow
+            };
+
+            lock (_connectedClientVersionsLock)
+            {
+                _connectedClientVersions[clientId] = info;
+            }
+
+            if (!string.IsNullOrEmpty(expectedVersion) && !string.Equals(expectedVersion, appVersion, StringComparison.OrdinalIgnoreCase))
+            {
+                this.LogWarning(
+                    "Client {clientId} (touchpanel {touchpanelKey}) reported UI app version {appVersion}, which does not match configured versions.touchpanelWrapperApp version {expectedVersion}",
+                    clientId, touchpanelKey, appVersion, expectedVersion
+                );
+            }
+            else
+            {
+                this.LogVerbose(
+                    "Client {clientId} (touchpanel {touchpanelKey}) reported UI app version {appVersion}",
+                    clientId, touchpanelKey, appVersion
+                );
+            }
+        }
+
         private void SendTouchpanelKey(string clientId, JToken touchpanelKeyToken)
         {
             if (touchpanelKeyToken == null)