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

src/ZB.MOM.WW.MxGateway.Server/Configuration/GatewayOptionsValidator.cs

@@ -470,7 +470,7 @@ public sealed class GatewayOptionsValidator : OptionsValidatorBase<GatewayOption
 
     // The worker-frame (pipe) maximum must stay above the public gRPC cap by the envelope-overhead
     // reserve, otherwise a maximally-sized accepted gRPC payload does not fit one worker frame once
-    // wrapped in a WorkerEnvelope and the outbound write faults the whole session (IPC-03). Fail fast
+    // wrapped in a WorkerEnvelope and the outbound write faults the whole session. Fail fast
     // at startup rather than mid-traffic. Only checked when both knobs are themselves in range so the
     // message is not doubled up with the individual range errors.
     private static void ValidateFrameSizeHeadroom(