For one luminous hour at SoHo Playhouse, Liz Coin builds a one-woman cathedral of positivity that admits everyone in the room. Lizzy Sunshine is part stand-up, part clown-show, part secular hymn for anyone who has ever loved someone struggling with addiction. Wear the rose-colored glasses. Sing along to “Tomorrow.” Get FaceTimed by Dad. Allow yourself to be undone by a comedian who refuses to look away from the heart. Then tell three friends — and a fourth, for luck.