ATLANTA — Josh Hart’s availability hangs in the balance for a pivotal Game 6.  The Knicks listed him as questionable with a lower back contusion as they look to close out their first-round series with the Hawks.  He subbed out with 6:27 left in the fourth quarter of the Knicks’ 126-97 Game 5 win Tuesday night at Madison Square Garden, went to the locker room and never returned to the bench. Earlier in the game, he could be seen holding his back in some pain.  Josh Hart speaks with Mikal Bridges during the Knicks’ Game 5 blowout win over the Hawks on April 28, 2026. JASON SZENES FOR THE NEW YORK POST Hart, despite his shooting woes, has had a strong series in every other department.…