docs(src): add missing XML docs and strip tracking-ID comments

Sweep of 203 source files resolving CommentChecker findings: add
<summary>/<param>/<returns>/<inheritdoc> where missing, and remove
resolved task/issue tracking markers (Tests-NNN, Worker-NNN, Server-NNN,
Task N) from code comments. Comment/doc-only — no logic changes.
Server+Tests build clean under TreatWarningsAsErrors.

src/ZB.MOM.WW.MxGateway.Server/Dashboard/IDashboardSnapshotService.cs

@@ -8,11 +8,13 @@ public interface IDashboardSnapshotService
     /// <summary>
     /// Gets the current dashboard snapshot.
     /// </summary>
+    /// <returns>The current dashboard snapshot.</returns>
     DashboardSnapshot GetSnapshot();
 
     /// <summary>
     /// Watches for changes to the dashboard state as an async enumerable.
     /// </summary>
     /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
+    /// <returns>An asynchronous stream of dashboard snapshots.</returns>
     IAsyncEnumerable<DashboardSnapshot> WatchSnapshotsAsync(CancellationToken cancellationToken);
 }