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.Tests/Security/Authentication/SqliteAuthStoreTests.cs

@@ -5,12 +5,14 @@ using Microsoft.Extensions.DependencyInjection;
 using ZB.MOM.WW.MxGateway.Server;
 using ZB.MOM.WW.MxGateway.Server.Configuration;
 using ZB.MOM.WW.MxGateway.Server.Security.Authentication;
+using ZB.MOM.WW.MxGateway.Tests.Gateway;
 
 namespace ZB.MOM.WW.MxGateway.Tests.Security.Authentication;
 
 /// <summary>
 /// Tests for <see cref="SqliteAuthStore"/>.
 /// </summary>
+[Collection(HostBuildingCollection.Name)]
 public sealed class SqliteAuthStoreTests : IDisposable
 {
     private readonly List<TempDatabaseDirectory> _tempDirectories = [];