When Vida Ghahremani became a movie star at age 16 in the Shah’s Iran, she felt as if she were in prison. It left her with a lifelong desire to pursue freedom at all costs, but the memory of those years made her burst out in uncontrollable tears during a rehearsal for her role as an Iranian exile in Wayne Wang’s superb new film A Thousand Years of Good Prayers, which opens this weekend in the Bay Area.