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

src/MxGateway.IntegrationTests/IntegrationTestEnvironmentTests.cs

@@ -2,6 +2,7 @@ namespace MxGateway.IntegrationTests;
 
 public sealed class IntegrationTestEnvironmentTests
 {
+    /// <summary>Verifies that live MXAccess tests use correct environment variable name.</summary>
     [Fact]
     public void LiveMxAccessTests_AreOptInByEnvironmentVariable()
     {
@@ -10,6 +11,7 @@ public sealed class IntegrationTestEnvironmentTests
             IntegrationTestEnvironment.LiveMxAccessVariableName);
     }
 
+    /// <summary>Verifies that worker executable uses correct environment variable name.</summary>
     [Fact]
     public void LiveMxAccessWorkerExecutable_UsesDocumentedEnvironmentVariable()
     {
@@ -18,6 +20,7 @@ public sealed class IntegrationTestEnvironmentTests
             IntegrationTestEnvironment.LiveMxAccessWorkerExecutableVariableName);
     }
 
+    /// <summary>Verifies that repository root resolution accepts git worktree files.</summary>
     [Fact]
     public void ResolveRepositoryRoot_AcceptsGitWorktreeFile()
     {