SimpleChat plugin validation endpoints missing authentication and authorization

SimpleChat is a secure AI conversation application with personal and group workspaces for document-grounded interactions. Prior to 0.241.206, several plugin validation routes in application/single_app/plugin_validation_endpoint.py, including `POST /api/admin/plugins/test-instantiation`, `GET /api/admin/plugins/health-check/<plugin_name>`, `POST /api/admin/plugins/repair/<plugin_name>`, and `POST /api/plugins/validate`, relied on @swagger_route(security=get_auth_security()) documentation without enforcing @login_required, @user_required, or @admin_required at runtime, allowing unauthenticated or unauthorized clients to invoke plugin validation, health, and repair behavior. This issue is fixed in version 0.241.206.