Its detractors call it the Eye of Sauron, and its defenders, “the guardian of Chihuahua.” The Sentinel Tower is a multi-million-dollar investment, a borderland’s bet on security. It’s the tallest building in Ciudad Juárez, that which best represents the fear of mass surveillance. And this week, it became a new battlefield in the political war between Mexican President Claudia Sheinbaum’s left-wing administration and the state government of the r…