New York City subway singer Just Sam is the newest “American Idol.”  The 20-year-old signer, whose real name is Samantha Diaz, delivered a knockout performance of Kelly Clarkson’s “Stronger” during last night’s season finale, which was the first one in history to be filmed at home.  She also performed Andra Day’s “Rise Up,” which will be released as a single.   And American Idol is coming back for another season.  ABC has renewed the singing competition show for a fourth season.