DETROIT — Valentine’s Day dinner at White Castle with candles, attentive wait staff and white tablecloths was a treasured experience for Krystal Gray and her mother, Cornelia Murphy. This year, Gray will bring along a photo of her mother, who died last spring at age 80, and place it on the table she has still reserved at one of the fast-food chain restaurants in the Detroit suburb of Ferndale. “It wouldn’t be the same without her,” Gray said. “I wanted something to make me feel better about her