SANTA CLARA, Calif. — It was the sort of tense, nail-biting win that had eluded the front-running 49ers all season, but it arrived at the perfect time. With their season on the line in the fourth quarter against the Green Bay Packers, the 49ers scored on a 6-yard run by Christian McCaffrey with 1:07 to play and escaped with a 24-21 divisional playoff win Saturday night at Levi’s Stadium. Dre Greenlaw’s interception of Jordan Love with 34 seconds to play sealed the verdict. The 49ers (13-5) are one step from a world championship for the third straight season and will face the winner of Sunday’s…