COMMERCE CITY — The Rapids concluded the most successful regular season in franchise history on Sunday, becoming the fifth team to go undefeated at home in the 21-year history of Major League Soccer, battling to a 1-1 tie with Houston. Colorado (15-6-13) could have won the league’s Supporters’ Shield with a win if FC Dallas had lost at Los Angeles in a game played simultaneously, but that game ended in a scoreless draw.