docs: add missing XML doc comments across gateway, worker, and .NET client

Resolves 1113 documentation-completeness gaps flagged by CommentChecker
(MissingReturns, MissingInheritDoc, InheritDocMisused, MissingDoc,
MissingParam, RedundantInheritDoc) so the API surface is fully documented
and the analyzer scan is clean. Doc comments only; no code changes.

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Cli/MxGatewayCliSecretRedactor.cs

@@ -6,6 +6,7 @@ internal static class MxGatewayCliSecretRedactor
     /// <summary>Replaces occurrences of the API key in the value with a redacted placeholder.</summary>
     /// <param name="value">The message text to redact.</param>
     /// <param name="apiKey">The API key to remove; no redaction if null or empty.</param>
+    /// <returns>The message text with any API key occurrence replaced by <c>[redacted]</c>.</returns>
     public static string Redact(string value, string? apiKey)
     {
         if (string.IsNullOrEmpty(value) || string.IsNullOrEmpty(apiKey))