With its fizzy essence, tart-sweet zing on the tongue and subtle notes of whatever fruit or herb it’s been infused with, kombucha is easing into the “mocktail” scene without overtly being the drink solely of nondrinkers. That’s what’s happening at Cross Culture Kombucha in Danbury, where the fermented tea drink - with roots that date to ancient China - is brewed onsite and offered on draft in a snug taproom.