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/DashboardGroupRoleMapping.cs

@@ -16,6 +16,7 @@ internal static class DashboardGroupRoleMapping
     /// </summary>
     /// <param name="groups">The collection of LDAP groups the user belongs to.</param>
     /// <param name="groupToRole">The mapping from group names to dashboard role names.</param>
+    /// <returns>The distinct set of dashboard roles matched from the user's groups.</returns>
     internal static IReadOnlyList<string> MapGroupsToRoles(
         IEnumerable<string> groups,
         IReadOnlyDictionary<string, string> groupToRole)
@@ -61,6 +62,7 @@ internal static class DashboardGroupRoleMapping
 
     /// <summary>Extracts the first RDN value from a distinguished name.</summary>
     /// <param name="distinguishedName">The LDAP distinguished name.</param>
+    /// <returns>The value portion of the first RDN component, or the full string if no <c>=</c> is found.</returns>
     internal static string ExtractFirstRdnValue(string distinguishedName)
     {
         int equalsIndex = distinguishedName.IndexOf('=');