The Bucktown Cuban restaurant Cafe Laguardia at 2111 W. Armitage Ave. is putting out all the stops for Valentine's Day, with a special not-yet-released food and cocktail menu and a free concert by Angel d'Cuba, former lead singer with Cuban super-group Mezcla.   d'Cuba performs at 8 p.m. and the restaurant closes at 11 p.m. Walk-ins welcome, though reservations can be made by calling 773-862-5996.