The Cow Creek Umpqua Tribe says it opposes a proposed casino in Medford because it would invade the market for the tribe’s Canyonville casino and violate an agreement that tribes in Oregon would limit their gambling outlets. The Coquille Indian Tribe, which operates the Mill Casino in North Bend, announced plans last week to open another casino in Medford. The Roseburg-based Cow Creek tribe, which owns the Seven Feathers Casino Resort in Canyonville, called the plans “disappointing and outrageous” in a statement issued Monday. “We see it as an infringement on our territory,” the Cow Creek tribal administrator and CEO, …