In 2006, at age 19, musician Zach Condon and his band Beirut exploded onto the indie-rock scene with a dramatic collection of Balkan-inspired arrangements for horn, ukulele, keyboards and strings. The bloggers raved, the venues got bigger, the haters left comments. But less than a year later, the teen’s too-sudden indie-rock apotheosis landed him in the hospital for “extreme exhaustion” and forced the cancellation of a tour that included sold-out dates at Bowery Ballroom. Condon......