Kathryn Steinle had just sent her mother a quintessential San Francisco picture — a photo of her, her father and a family friend on the scenic waterfront of the Embarcadero. But five minutes later, with her father’s arm around her shoulder, the 32-year-old Pleasanton native suddenly collapsed on Pier 14 just south of the Ferry Building. It was 6:30 p.m. Wednesday, and she had been struck in the chest by a bullet.