client/dotnet: backfill XML doc comments to satisfy analyzers

Adds missing <summary>/<param> docs across the .NET client library and its
test suite so CommentChecker reports zero issues. TreatWarningsAsErrors
requires the analyzer surface clean before publishing the NuGet package.

clients/dotnet/ZB.MOM.WW.MxGateway.Client/GalaxyRepositoryClient.cs

@@ -182,6 +182,10 @@ public sealed class GalaxyRepositoryClient : IAsyncDisposable
         return await DiscoverHierarchyAsync(new DiscoverHierarchyOptions(), cancellationToken).ConfigureAwait(false);
     }
 
+    /// <summary>Discovers the Galaxy object hierarchy.</summary>
+    /// <param name="options">Client configuration options.</param>
+    /// <param name="cancellationToken">Token to observe for cancellation.</param>
+    /// <returns>The collection of Galaxy objects in the hierarchy.</returns>
     public async Task<IReadOnlyList<GalaxyObject>> DiscoverHierarchyAsync(
         DiscoverHierarchyOptions options,
         CancellationToken cancellationToken = default)