refactor(logging): adopt ZB.MOM.WW.Telemetry.Serilog bootstrap

Swap the gateway process logging from the default Microsoft.Extensions.Logging
provider onto the shared ZB.MOM.WW.Telemetry.Serilog two-stage bootstrap.

- Add a cross-repo ProjectReference to ZB.MOM.WW.Telemetry.Serilog (transitively
  brings the Telemetry core package); the referenced project resolves its own
  Directory.Build.props / Directory.Packages.props so it does not perturb this build.
- Replace MEL wiring in GatewayApplication with builder.AddZbSerilog(ServiceName=
  "mxgateway"; SiteId/NodeRole read from MxGateway:Telemetry when present) and add
  app.UseSerilogRequestLogging().
- Add a Serilog section (Console + daily rolling File sinks, MinimumLevel) to
  appsettings.json and a MinimumLevel override to appsettings.Development.json,
  replacing the old MEL Logging sections.

The net48/x86 worker is untouched. Correlation scope + redaction move to the
shared ILogRedactor seam in the follow-up commit.

src/ZB.MOM.WW.MxGateway.Server/appsettings.json

@@ -1,9 +1,30 @@
 {
-  "Logging": {
-    "LogLevel": {
+  "Serilog": {
+    "Using": [
+      "Serilog.Sinks.Console",
+      "Serilog.Sinks.File"
+    ],
+    "MinimumLevel": {
       "Default": "Information",
-      "Microsoft.AspNetCore": "Warning"
-    }
+      "Override": {
+        "Microsoft.AspNetCore": "Warning"
+      }
+    },
+    "WriteTo": [
+      {
+        "Name": "Console",
+        "Args": {
+          "outputTemplate": "[{Timestamp:HH:mm:ss} {Level:u3}] [{NodeRole}/{NodeHostname}] {Message:lj} {Properties:j}{NewLine}{Exception}"
+        }
+      },
+      {
+        "Name": "File",
+        "Args": {
+          "path": "logs/mxgateway-.log",
+          "rollingInterval": "Day"
+        }
+      }
+    ]
   },
   "AllowedHosts": "*",
   "MxGateway": {