After five days, the Gardner family was wondering whether Shadow, their beloved five-year-old pug, would ever return to his Lagunitas home. Grim possibilities arose: Was he hit by a car? Snatched by a coyote? Maybe even dognapped? It wasn’t like him to wonder off for long. But after they posted on Nextdoor and Instagram, neighbors quickly rallied. “Everybody in our tight-knit little community was rooting for Shadow to make it,” said Steve Gardner, who spent…