LAVEEN VILLAGE, Arizona — President Joe Biden on Friday formally apologized to Native Americans for the government-run boarding school system that for decades forcibly separated children from their parents, calling it a “blot on American history” in his first presidential visit to Indian Country. “It’s a sin on our soul,” said Biden, his voice full of anger and emotion. “Quite frankly, there’s no excuse that this apology took 50 years to make.” It was a moment of both contrition and frustration as the president sought to recognize one of the “most horrific chapters” in the national story. Biden spoke of