Captain Marvel” has one job. That job is to explain the origin story of its titular shero well enough to justify her role in saving the universe when “Avengers: Endgame” opens on April 26.At the climax of “Avengers: Infinity War,” tough-love villain Thanos disintegrated half the universe (ostensibly for its own good), including a critical mass of Marvel superheroes. Someone else super will have to step in to put things right.Which explains why the good folks at Marvel dug into the comic …