feat(07-07): add DI registrations for Phase 7 services and create UserAccessAuditView

- Register IUserAccessAuditService, IGraphUserSearchService, export services, ViewModel and View in App.xaml.cs
- Create UserAccessAuditView.xaml with two-panel layout: people picker, site picker, scan options, color-coded DataGrid with grouping, summary banner
- Create UserAccessAuditView.xaml.cs code-behind with ViewModel constructor injection
- [Rule 3] UserAccessAuditView was missing (07-05 not executed); created inline to unblock 07-07

SharepointToolbox/App.xaml.cs

@@ -151,6 +151,14 @@ public partial class App : Application
         services.AddTransient<FolderStructureViewModel>();
         services.AddTransient<FolderStructureView>();
 
+        // Phase 7: User Access Audit
+        services.AddTransient<IUserAccessAuditService, UserAccessAuditService>();
+        services.AddTransient<IGraphUserSearchService, GraphUserSearchService>();
+        services.AddTransient<UserAccessCsvExportService>();
+        services.AddTransient<UserAccessHtmlExportService>();
+        services.AddTransient<UserAccessAuditViewModel>();
+        services.AddTransient<UserAccessAuditView>();
+
         services.AddSingleton<MainWindow>();
     }
 }