chore(lmxproxy): switch health probe tag to DevAppEngine.Scheduler.ScanTime, remove temp prompts

AppEngine built-in tag is always present and constantly updating (~1s),
making it a more reliable probe than a user-deployed TestChildObject tag.

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

lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/Configuration/LmxProxyConfiguration.cs

@@ -31,8 +31,8 @@ namespace ZB.MOM.WW.LmxProxy.Host.Configuration
     /// <summary>Health check / probe configuration.</summary>
     public class HealthCheckConfiguration
     {
-        /// <summary>Tag address to probe for connection liveness. Default: TestChildObject.TestBool.</summary>
-        public string TestTagAddress { get; set; } = "TestChildObject.TestBool";
+        /// <summary>Tag address to probe for connection liveness. Default: DevAppEngine.Scheduler.ScanTime.</summary>
+        public string TestTagAddress { get; set; } = "DevAppEngine.Scheduler.ScanTime";
 
         /// <summary>Probe timeout in milliseconds. Default: 5000.</summary>
         public int ProbeTimeoutMs { get; set; } = 5000;

lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/Health/DetailedHealthCheckService.cs

@@ -20,7 +20,7 @@ namespace ZB.MOM.WW.LmxProxy.Host.Health
 
         public DetailedHealthCheckService(
             IScadaClient scadaClient,
-            string testTagAddress = "TestChildObject.TestBool")
+            string testTagAddress = "DevAppEngine.Scheduler.ScanTime")
         {
             _scadaClient = scadaClient;
             _testTagAddress = testTagAddress;

lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/appsettings.json

@@ -33,7 +33,7 @@
   },
 
   "HealthCheck": {
-    "TestTagAddress": "TestChildObject.TestBool",
+    "TestTagAddress": "DevAppEngine.Scheduler.ScanTime",
     "ProbeTimeoutMs": 5000,
     "MaxConsecutiveTransportFailures": 3,
     "DegradedProbeIntervalMs": 30000