DAYTON, Ohio — The 50-yard line of Welcome Stadium, the home field of Dayton’s five public high school football teams, sits just a few Hail Marys from the west bank of the river that bisects the city. The Great Miami River — overwhelmingly Black on the west side, overwhelmingly White on the east — has long symbolized Dayton’s acute divisions by any number of metrics: race, income, life expectancy, access to healthy food.