Workers returned Tuesday to the job at Stella D’Oro Biscuit Co. in the Bronx after a judge ordered the company reinstate the 136 employees who had remained strong throughout a brutal 11-month strike. But before they could even walk through the doors, they were greeted with the anti-union response by the company’s private equity firm owners, the 21st century’s mutation of the robber barons: Brynwood Partners announced it would shut down operations in October.