docs: add missing XML doc comments across gateway, worker, and .NET client

Resolves 1113 documentation-completeness gaps flagged by CommentChecker
(MissingReturns, MissingInheritDoc, InheritDocMisused, MissingDoc,
MissingParam, RedundantInheritDoc) so the API surface is fully documented
and the analyzer scan is clean. Doc comments only; no code changes.

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

@@ -6,6 +6,7 @@ public sealed class DashboardApiKeyAuthorization
 {
     /// <summary>Determines whether the user can manage API keys.</summary>
     /// <param name="user">The authenticated user principal.</param>
+    /// <returns>True if the user is an authenticated admin; otherwise false.</returns>
     public bool CanManage(ClaimsPrincipal user)
     {
         if (user.Identity?.IsAuthenticated != true)