“Blood Brothers,” the 81-minute iQIYI quickie that dropped on 5 October , is exactly the kind of urban-migrant morality play the algorithm orders when it smells a holiday weekend and a social-media hashtag. Liu Lang, our wronged-gaokao hero, is sketched with the same thick Sharpie the film uses for everything else: one minute he’s tearing up an exam permit in the world’s least convincing slow-motiver mais...