“Integrative medicine” has become a hot concept in the wellness biz over the past few years, but it turns out that decades ago, the playwright Lisa Kron’s mom pioneered a more literal and very specific try at the idea: Better health through racial integration. That’s just one of the topics Kron explores in her 2006 piece “Well,” a surprising, often comical and freewheeling work now getting its San Diego premiere at Diversionary Theatre.