The new Brazilian film “I’m Still Here” begins with images often associated with the country: the gorgeous grin of Rio’s shoreline, totemic Sugarloaf Mountain, beach volleyball, and sunbathers galore. Yet this idyllic vibe comes under shadow briefly, when a military helicopter cuts through the air above our heroine, Eunice, as she’s floating on her back in the water. A little later on, another disturbance of the blissful ambience occurs when Eunice’s teenage daughter Vera and three of her friends encounter a police checkpoint while driving through a city tunnel.