The home Elke Koller chose for her retirement has horse pastures and bird song, a tranquil garden where her grandchildren love to play and views that stretch for miles across the green hills of western Germany’s Eifel region. It is also close enough to a stash of nuclear weapons at a joint U.S.-German base that should they detonate, she would be vaporized within seconds. “It’s so nice here. I didn’t…