AI Assistant (Abby)POST /api/v1/abby/create-cohort Parse NL prompt → build cohort expression → persist CohortDefinition.POST /api/v1/abby/create-cohort Parse NL prompt → build cohort expression → persist CohortDefinition. POST /api/v1/abby/create-cohort Returns the saved cohort + full build output for immediate UI display. Request Responses401