Everything's "coming up roses" this month for the girl who's about to be a bride. Cupcakes are in bloom with pink frosting flowers; paper posies are budding on party trees; and in the punch bowl, a splash of rose water lends its delicate fragrance and flavor. Who's behind the rosey glow?- you, of course, with your green party thumb, coordinating the prettiest shower of the season for a friend who is going to be married.