SAN MARINO, Calif. — Like many designers, Ralph Lauren is a cinephile, whose vision for his brand is theatrical in scope: a movie with infinite sequels. But he is decidedly East Coast in his sensibility, and has never shown a collection in Los Angeles until Thursday evening. What felt like a last bastion of the Hollywood A-List — longtime house muse Diane Keaton, Jennifer Lopez and Ben Affleck, Ashton Kutcher and Mila Kunis, Sylvester…