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.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 value with any occurrences of <paramref name="apiKey"/> replaced by a redacted placeholder.</returns>
     public static string Redact(string value, string? apiKey)
     {
         if (string.IsNullOrEmpty(value) || string.IsNullOrEmpty(apiKey))