DETROIT — They came for a concert and ended up at a wedding. Jack White capped off a legendary day in his hometown on Friday by getting engaged and then married on stage to his girlfriend, singer Olivia Jean, in front of a sold-out crowd at Detroit’s Masonic Temple on the first night of his Supply Chain Issues tour. White brought Jean on stage for a duet of the White Stripes’ 2001 hit “Hotel Yorba.” He introduced Jean to the crowd as his girlfriend, and then told her he had a question for her. “Yeah?” she asked, her voice making it apparent it was not a rehearsed bit. “Will you marry me?” he a…