Suddenly, all bets are on regarding the future of American sports gambling. A surge in betting caused by the Supreme Court’s lifting of a federal ban on sports wagering is expected to trigger new gaming opportunities and burnish existing sports books in Las Vegas casinos — but also spawn a battle in California among horse-racing tracks, Indian casinos and card clubs as they try to grab a slice of the added action. “We are excited and we are ready to roll on this,” said Ernest Stevens Jr., chairman of the National Indian Gaming Assn., a trade group for Indian casinos....