At first glance, Cargill has the right résumé: He started at Cheers. Of course, he was only parking cars. Now behind the bar at a more upscale and off-the-beaten-path location, the Newburyport native has quietly made a name for himself, especially for his mojitos. (He’s got the muddler’s callous to prove it.) But he’s equally adept at martinis or whatever might be your highball poison. Cargill’s laid-back charisma and cackling laugh perfectly match Chez Henri’s easygoing French-Cuban vibe, and his knack for creative mixology produces concoctions that would bowl over even Norm Peterson.