Once a week, a little past noon on Wednesdays, a line of cars forms outside the wrought-iron gates of the Carolands mansion, 20 miles south of downtown San Francisco. From the entrance, you can see the southeast facade of the 98-room Beaux Arts chateau, which was built a century ago by an heiress to the Pullman railroad-car fortune. Not visible from that vantage point is the stately reflecting…