Armed with research showing that casual dress at work has hampered productivity, a bold new movement called Dress Up Thursdays is emerging to get Americans to shape up sartorially. "Casual dressing . . . has been allowed in too many office settings to degenerate into ‘sloppy casual’ or ‘weekend casual,’ " notes the group’s Web site (www.1dressup.com). But don’t look for frustrated CEOs or indignant stockholders behind this "grassroots" crusade. It’s being mobilized by the real losers in the casual office revolution: the men’s clothing industry.