docs: complete XML-doc coverage and strip internal tracking IDs from code comments

Resolve all CommentChecker findings across the gateway server, worker, tests,
and .NET client (314 -> 0 real issues): add missing <returns>/<summary>/<param>
on public and test members, convert Stream/interface overrides to <inheritdoc/>,
and remove internal task/issue tracking IDs (SEC-*, IPC-*, WRK-*, GWC-*, TST-*,
Client.Dotnet-*) from shipped code documentation while preserving the design
rationale prose. Shipped comments should not carry internal bookkeeping, and
complete XML docs keep the analyzer/TreatWarningsAsErrors gate and generated API
docs clean. The 6 remaining flags are heuristic false positives (MD5, UTC-4,
capacity-1, near-1601) left intact so real documentation is not corrupted.

Claude-Session: https://claude.ai/code/session_01DMXXvNuPekkkrTEyPNxEkW

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

@@ -249,6 +249,7 @@ public sealed class MxGatewayClient : IAsyncDisposable
     /// <summary>
     /// Disposes the client and releases all resources.
     /// </summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     public ValueTask DisposeAsync()
     {
         if (_disposed)
@@ -318,6 +319,11 @@ public sealed class MxGatewayClient : IAsyncDisposable
     private static HttpMessageHandler CreateHttpHandler(MxGatewayClientOptions options) =>
         CreateHttpHandlerForTests(options);
 
+    /// <summary>
+    /// Creates the <see cref="SocketsHttpHandler"/> used for gRPC calls; exposed internally so tests can inspect it.
+    /// </summary>
+    /// <param name="options">The client options that configure connect timeout and TLS behavior.</param>
+    /// <returns>A configured <see cref="SocketsHttpHandler"/>.</returns>
     internal static SocketsHttpHandler CreateHttpHandlerForTests(MxGatewayClientOptions options)
     {
         SocketsHttpHandler handler = new()