To the smartphone-addled among us, advising the use of apps to fix mental health problems might seem like telling someone who needs to get fit to live on jam and fags. But it’s happening all the same. While gadget and social media addiction are lampooned for increasing teenage depression, and complaints abound that the constant compulsion to check apps and message conduits leaves us frazzled and scatterbrained, purveyors of wearable tech, app designers and even…