“Who’s zoomin’ who?” asked Aretha Franklin in her 1985 hit of the same name — and while the song doesn’t feature amid the film’s cooler musical selections, it summarizes the key dramatic question of “Zoom.” A spirited if spotty solo debut for Brazilian helmer Pedro Morelli, this breathless trifle triangulates the personal and creative crises of an insecure comic-book artist, a cocksure filmmaker and an aspiring novelist — with the considerable