“ The Garden We Dreamed ” opens on a complex symphony of natural sound: layer upon layer of birdsong, insect chatter and weather-rustled foliage, all the more intensified for playing out over a virtually dark screen. It’s barely the first light of dawn in the forested wilds of central Mexico, as the camera pans across treetops just discernible from the charred sky above them, and we’re reminded that nature, even at its most tranquil, is never quiet. Still, it’s drowned out in short order by the