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.Tests/Gateway/Grpc/EventStreamServiceTests.cs

@@ -39,7 +39,7 @@ public sealed class EventStreamServiceTests
     }
 
     /// <summary>
-    ///     TST-02 (owner-scoped attach): the API key that opened a session may attach its event
+    ///     Owner-scoped attach: the API key that opened a session may attach its event
     ///     stream — the caller key equals the session owner, so streaming proceeds normally.
     /// </summary>
     /// <returns>A task that represents the asynchronous operation.</returns>
@@ -64,7 +64,7 @@ public sealed class EventStreamServiceTests
     }
 
     /// <summary>
-    ///     TST-02 (owner-scoped attach, security control): a caller whose API key differs from
+    ///     Owner-scoped attach, security control: a caller whose API key differs from
     ///     the key that opened the session is rejected with a <see cref="SessionManagerErrorCode.PermissionDenied"/>
     ///     fault before any events are streamed — closing the reconnect/fan-out trust-boundary hole.
     /// </summary>