EXCLUSIVE TO YOU IN YOUR CITY   SPOOKY GROUNDS -- William Gaunt (left) and Stuart Damon, as Nemesis’ ace agents, investigate the surroundings of a British manor house whose mistress practices witchcraft in “The Night People” episode of “The Champions,” to be colorcast on the NBC Television Network Monday, August 12 (8-9 p.m. NYT)   (C)   NBC-TV CAPTION SUBJECT:     William Gaunt (left) and Stuart Damon PROGRAM:     “The Night People” episode colorcast of “The Champions” TIME:     NBC Television Network, Monday, August 12 (8-9 p.m. NYT)