ISTANBUL — If you stand in the center of the Hagia Sophia here and gaze upward at what is one of the world’s tallest domes, you can be staggered by the overlapping layers of ruination and grandeur in this Church of Holy Wisdom. And I don’t just mean the scaling paint, the scaffolding promising overdue restorations, the haunting mosaics disclosed under layers of plaster. For a millennium after its construction in the sixth century, this was the world’s largest cathedral, the most prominent monument to Byzantine Christianity. And it still manages to seem delicate and…