docs: strip task-tracking IDs from code comments and fill missing XML docs

Tracking IDs are review bookkeeping that rots in shipped source; the rationale they tagged is kept. Comment-only change (CommentChecker 458 -> 16 false positives).

src/ZB.MOM.WW.MxGateway.Server/Grpc/EventStreamService.cs

@@ -116,7 +116,7 @@ public sealed class EventStreamService(
         // its `yield return` is what feeds the gRPC writer.
         ChannelReader<MxEvent> reader = subscriber.Reader;
 
-        // GWC-15: register this subscriber's channel as a live backlog source instead of
+        // Register this subscriber's channel as a live backlog source instead of
         // reconciling the queue-depth gauge on every event. The gauge previously read the
         // bounded channel's Count (which takes the channel's internal lock) and adjusted the
         // metric under its own lock on every streamed event. Now the metric reads Count only
@@ -197,7 +197,7 @@ public sealed class EventStreamService(
                     }
 
                     // The queue-depth gauge is maintained lazily via the backlog registration
-                    // above (GWC-15): the metric reads this subscriber's channel Count only when
+                    // above: the metric reads this subscriber's channel Count only when
                     // scraped, so there is no per-event gauge bookkeeping on this hot path.
                     yield return mxEvent;
                 }