That would give the Niners much-needed veteran leadership upfront CBS Sports went through each NFL roster to determine one move they should make before the season kicks off. Of course, the 49ers need to extend Deebo Samuel and figure out what to do with Jimmy Garoppolo, but that’s not the direction CBS went. They believe it’s in the Niners’ best interest to sign former Browns center J.C. Tretter: Alex Mack’s retirement changes the complexion of the San Francisco 49ers’ offensive line. Plenty of talent still exists among the group, of course, particularly with left tackle Trent Williams. However, Mack served…