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/DashboardServiceCollectionExtensions.cs

@@ -25,6 +25,7 @@ public static class DashboardServiceCollectionExtensions
     /// from the <c>MxGateway:Ldap</c> section. Also read to select the dashboard
     /// authentication scheme via the <c>MxGateway:Dashboard:DisableLogin</c> dev flag.
     /// </param>
+    /// <returns>The service collection, for chaining.</returns>
     public static IServiceCollection AddGatewayDashboard(
         this IServiceCollection services,
         IConfiguration configuration)