The Dog Day Harvest Costume Parade and Party, held at the Washington Square Park fountain on Nov. 19, featured treats, vendors, costumes, prizes, artists, trainers, vets and even a dog psychic. Up for grabs were a Nantucket weekend and thousands of dollars in prizes. But the main thing — at least for those pooches who weren’t too annoyed at being garbed in goofy getups — is that it was a lot of tail-wagging fun.