Christy Sports, the Colorado retailer that has done the most in recent years to preserve the tradition of Labor Day ski and snowboard sales, will cut a different line this year by shifting those sales to a primarily online format. For the past 13 years, Powder Daze lured Front Range skiers and snowboarders during the summer heat to its Littleton store, which would be crammed with last year’s skis, boards and boots at clearance prices.