Ghost sightings in the theater usually mean Henrik Ibsen or a despondent Danish prince. A total fleece, in other words, if you’re a kid or can still think like one. But “Paranormal Activity,” an itinerant amusement at Shakespeare Theatre Company’s Harman Hall that’s as much a carnival-style haunted house as a domestic drama about a troubled marriage, will give even the most lizard-brained aesthetes among us their money’s worth and then some. If you’re game to have your soul harrow’d up and yer young blood froze by something other than the news, you are invited.