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;