A mortal chill runs through “Here We Go,’’ a spare and haunting drama about the end of life. And the journey to the grave is no picnic, either, given how susceptible we are to the kind of bad faith, manipulation, and deceit that undergird “Blue Kettle.’’ All in all, it’s not a cheery vision of human existence delivered by this pair of one-act plays. But when the creator of that vision is as brilliantly persuasive and original as British dramatist Caryl Churchill, you tend to get drawn inexorably into not just her world but her worldview.