feat(17-01): register ISharePointGroupResolver in DI container (App.xaml.cs)

SharepointToolbox/App.xaml.cs

@@ -158,6 +158,9 @@ public partial class App : Application
         services.AddTransient<FolderStructureViewModel>();
         services.AddTransient<FolderStructureView>();
 
+        // Phase 17: Group Expansion
+        services.AddTransient<ISharePointGroupResolver, SharePointGroupResolver>();
+
         // Phase 7: User Access Audit
         services.AddTransient<IUserAccessAuditService, UserAccessAuditService>();
         services.AddTransient<IGraphUserSearchService, GraphUserSearchService>();