“Oh, there’s my AirPod,” says Leighton Meester, scooping up the errant headphone that falls out of the pocket of her loose button-down shirt as she settles into a picnic table at Blueys, a laid-back cafe in Santa Monica whose patrons, on a recent Tuesday, don’t seem to recognize the 39-year-old in mom garb as the one-time ingénue who terrified the Parents Television Council (and titillated everyone else) when she appeared on billboards topless in a pool with her arms thrown passionately...