Add XML documentation across gateway, worker, and .NET client

clients/dotnet/MxGateway.Client/MxAccessException.cs

@@ -2,8 +2,13 @@ using MxGateway.Contracts.Proto;
 
 namespace MxGateway.Client;
 
+/// <summary>Exception thrown when an MXAccess command fails with a non-zero HResult or failing status.</summary>
 public sealed class MxAccessException : MxGatewayCommandException
 {
+    /// <summary>Initializes a new instance with the given message, reply, and optional inner exception.</summary>
+    /// <param name="message">The error message describing the MXAccess failure.</param>
+    /// <param name="reply">The MxCommandReply containing the failure details (statuses, HResult, etc.).</param>
+    /// <param name="innerException">The underlying exception, if any.</param>
     public MxAccessException(
         string message,
         MxCommandReply reply,
@@ -20,5 +25,6 @@ public sealed class MxAccessException : MxGatewayCommandException
         Reply = reply;
     }
 
+    /// <summary>Gets the underlying MxCommandReply containing full failure details.</summary>
     public MxCommandReply Reply { get; }
 }