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.Tests/Metrics/GatewayMetricsTests.cs

@@ -19,11 +19,11 @@ public sealed class GatewayMetricsTests
         metrics.CommandFailed("WriteSecured", "AuthorizationFailed", TimeSpan.FromMilliseconds(12));
         metrics.EventReceived("session-1", "OnDataChange");
         metrics.EventReceived("session-1", "OnDataChange");
-        // PERF-02: the worker queue-depth gauge sums one live source per worker client, so the two
+        // The worker queue-depth gauge sums one live source per worker client, so the two
         // registrations below stand in for two concurrent sessions holding 3 and 4 events.
         using IDisposable workerDepthSourceA = metrics.RegisterWorkerEventQueueDepthSource(static () => 3);
         using IDisposable workerDepthSourceB = metrics.RegisterWorkerEventQueueDepthSource(static () => 4);
-        // GWC-15: the gRPC stream queue-depth gauge sums live backlog sources at collection time
+        // The gRPC stream queue-depth gauge sums live backlog sources at collection time
         // rather than tracking a pushed running total. Register a source reporting 3.
         using IDisposable backlogSource = metrics.RegisterEventStreamBacklogSource(static () => 3);
         metrics.QueueOverflow("session-events");
@@ -58,7 +58,7 @@ public sealed class GatewayMetricsTests
     }
 
     /// <summary>
-    ///     PERF-02: the worker queue-depth gauge sums every registered source rather than holding a
+    ///     The worker queue-depth gauge sums every registered source rather than holding a
     ///     single pushed scalar, so concurrent sessions add up instead of overwriting one another,
     ///     and a disposed registration (a worker client going away) drops out of the sum. Disposal
     ///     is idempotent because a client's dispose path can run twice.