Next month at the Frankfurt auto show in Germany, Audi Audi, the surging premium-car division of Volkswagen, will show a battery-powered “concept” crossover SUV that’s a direct shot across the bow of electric-car innovator Tesla. In fact, if Tesla (TSLA) doesn’t find a way to damage-control the almost inevitable off-the-charts reaction to Audi’s super-slick e-tron quattro concept, it may markedly undercut the long-term prospects for Tesla’s own Model X crossover, for which anticipation has been…