Fox is lowering the curtain on “American Idol,” ending a series that dominated television throughout the 2000s and made stars of the likes of Simon Cowell, Kelly Clarkson and Carrie Underwood. The network announced Monday that “American Idol” will go off the air after its 15th season next spring. The cast from the past seasons, with Ryan Seacrest as host and Jennifer Lopez, Keith Urban and Harry Connick Jr. as judges, will return for a season-long celebration of the show’s history. “American Idol” faded over the past few years, eclipsed in the music competition genre it pioneered by “The Voice”...