refactor(logging): correlation scope + redaction on shared ILogRedactor seam

Move the per-request correlation context and secret redaction off the MEL
mechanism onto the Serilog primitives the shared bootstrap consumes.

- GatewayRequestLoggingMiddlewareExtensions now pushes the correlation
  properties (SessionId / WorkerProcessId / CorrelationId / CommandMethod /
  ClientIdentity) via Serilog LogContext.PushProperty for the request lifetime
  and pops them on completion, replacing MEL ILogger.BeginScope. Header parsing
  and property names are unchanged; GatewayLogScope remains the data holder.
- Add GatewayLogRedactorAdapter : ILogRedactor delegating to the existing
  GatewayLogRedactor policy (mxgw_ bearer tokens / credential-bearing command
  values), registered as a singleton so the shared RedactionEnricher masks
  secrets on every event. Remove the now-dead GatewayLoggerExtensions MEL helper.
- Tests: add GatewayLogRedactorAdapterTests; serialize the four host-building
  test classes into one non-parallel collection (HostBuildingCollection) so the
  process-wide Serilog bootstrap logger is not frozen by two concurrent host
  builds racing in parallel collections.

The net48/x86 worker is untouched.

src/ZB.MOM.WW.MxGateway.Server/Diagnostics/GatewayRequestLoggingMiddlewareExtensions.cs

@@ -1,4 +1,5 @@
 using Microsoft.Extensions.Primitives;
+using Serilog.Context;
 
 namespace ZB.MOM.WW.MxGateway.Server.Diagnostics;
 
@@ -17,7 +18,12 @@ public static class GatewayRequestLoggingMiddlewareExtensions
     /// <summary>Header name for the command method name.</summary>
     public const string CommandMethodHeaderName = "x-command-method";
 
-    /// <summary>Adds gateway request logging scope middleware that reads correlation headers and redacts sensitive data.</summary>
+    /// <summary>
+    /// Adds gateway request logging middleware that reads the correlation headers and pushes them
+    /// as Serilog <see cref="LogContext"/> properties for the duration of the request. The pushed
+    /// properties (SessionId / WorkerProcessId / CorrelationId / CommandMethod / ClientIdentity)
+    /// are disposed when the request completes; the shared redaction enricher masks any secrets.
+    /// </summary>
     /// <param name="app">Application builder.</param>
     public static IApplicationBuilder UseGatewayRequestLoggingScope(this IApplicationBuilder app)
     {
@@ -25,21 +31,56 @@ public static class GatewayRequestLoggingMiddlewareExtensions
 
         return app.Use(async (context, next) =>
         {
-            ILogger logger = context.RequestServices
-                .GetRequiredService<ILoggerFactory>()
-                .CreateLogger("MxGateway.Request");
-
-            using IDisposable? scope = logger.BeginGatewayScope(new GatewayLogScope(
+            GatewayLogScope scope = new(
                 SessionId: ReadHeader(context, SessionIdHeaderName),
                 WorkerProcessId: ReadInt32Header(context, WorkerProcessIdHeaderName),
                 CorrelationId: ReadUInt64Header(context, CorrelationIdHeaderName),
                 CommandMethod: ReadHeader(context, CommandMethodHeaderName),
-                ClientIdentity: ReadHeader(context, "authorization")));
+                ClientIdentity: ReadHeader(context, "authorization"));
+
+            using IDisposable correlationScope = PushCorrelationProperties(scope);
 
             await next(context);
         });
     }
 
+    /// <summary>
+    /// Pushes the populated <paramref name="scope"/> properties onto the Serilog
+    /// <see cref="LogContext"/>, returning a single disposable that pops them all when the request
+    /// completes. Only the properties present in <see cref="GatewayLogScope.ToDictionary"/> (which
+    /// already applies the client-identity redaction policy) are pushed.
+    /// </summary>
+    /// <param name="scope">The correlation properties for the current request.</param>
+    /// <returns>A disposable that removes the pushed properties on disposal.</returns>
+    private static IDisposable PushCorrelationProperties(GatewayLogScope scope)
+    {
+        Stack<IDisposable> pushed = new();
+
+        foreach (KeyValuePair<string, object?> property in scope.ToDictionary())
+        {
+            pushed.Push(LogContext.PushProperty(property.Key, property.Value));
+        }
+
+        return new CorrelationPropertyScope(pushed);
+    }
+
+    /// <summary>
+    /// Disposes the pushed <see cref="LogContext"/> property bindings in reverse order, restoring
+    /// the ambient context to its pre-request state.
+    /// </summary>
+    private sealed class CorrelationPropertyScope(Stack<IDisposable> bindings) : IDisposable
+    {
+        private readonly Stack<IDisposable> _bindings = bindings;
+
+        public void Dispose()
+        {
+            while (_bindings.Count > 0)
+            {
+                _bindings.Pop().Dispose();
+            }
+        }
+    }
+
     private static string? ReadHeader(HttpContext context, string headerName)
     {
         return context.Request.Headers.TryGetValue(headerName, out StringValues values)