Sombr surprised Lollapalooza fans in Chicago on Thursday night, bringing out 5 Seconds of Summer during his high-octane set, joining forces for “She Looks So Perfect.” The raucous performance came amid an already thrilling set that found the singer — clad in all-black with a lace T-shirt, feather-adorned coat, and boa — cooly pulling up in a car from backstage, drink in hand, to the massive audience that filled the field. “Chicago, you ready for…