feat: expand mqtt varz monitoring with all Go-compatible fields

src/NATS.Server/Monitoring/Varz.cs

@@ -355,8 +355,29 @@ public sealed class MqttOptsVarz
     [JsonPropertyName("port")]
     public int Port { get; set; }
 
+    [JsonPropertyName("no_auth_user")]
+    public string NoAuthUser { get; set; } = "";
+
+    [JsonPropertyName("auth_timeout")]
+    public double AuthTimeout { get; set; }
+
+    [JsonPropertyName("tls_map")]
+    public bool TlsMap { get; set; }
+
     [JsonPropertyName("tls_timeout")]
     public double TlsTimeout { get; set; }
+
+    [JsonPropertyName("tls_pinned_certs")]
+    public string[] TlsPinnedCerts { get; set; } = [];
+
+    [JsonPropertyName("js_domain")]
+    public string JsDomain { get; set; } = "";
+
+    [JsonPropertyName("ack_wait")]
+    public long AckWait { get; set; }
+
+    [JsonPropertyName("max_ack_pending")]
+    public ushort MaxAckPending { get; set; }
 }
 
 /// <summary>

src/NATS.Server/Monitoring/VarzHandler.cs

@@ -121,6 +121,7 @@ public sealed class VarzHandler : IDisposable
                 Subscriptions = _server.SubList.Count,
                 ConfigLoadTime = _server.StartTime,
                 HttpReqStats = stats.HttpReqStats.ToDictionary(kv => kv.Key, kv => (ulong)kv.Value),
+                Mqtt = BuildMqttVarz(),
             };
         }
         finally
@@ -134,6 +135,27 @@ public sealed class VarzHandler : IDisposable
         _varzMu.Dispose();
     }
 
+    private MqttOptsVarz BuildMqttVarz()
+    {
+        var mqtt = _options.Mqtt;
+        if (mqtt is null)
+            return new MqttOptsVarz();
+
+        return new MqttOptsVarz
+        {
+            Host = mqtt.Host,
+            Port = mqtt.Port,
+            NoAuthUser = mqtt.NoAuthUser ?? "",
+            AuthTimeout = mqtt.AuthTimeout,
+            TlsMap = mqtt.TlsMap,
+            TlsTimeout = mqtt.TlsTimeout,
+            TlsPinnedCerts = mqtt.TlsPinnedCerts?.ToArray() ?? [],
+            JsDomain = mqtt.JsDomain ?? "",
+            AckWait = (long)mqtt.AckWait.TotalNanoseconds,
+            MaxAckPending = mqtt.MaxAckPending,
+        };
+    }
+
     /// <summary>
     /// Formats a TimeSpan as a human-readable uptime string matching Go server format.
     /// </summary>