By ALEXANDRA E. PETRI Ariana Grande will curtail public appearances after her current world tour wraps up in September, citing “endless, ongoing public scrutiny” as a reason for her “much-needed break,” according to a statement issued on her behalf. Grande, 33, who is in Chicago for her Eternal Sunshine Tour, “will be taking a step back from visibility” after the tour concludes in London, a representative for the singer said Sunday. “She looks forward to finishing the tour and ending it on a…