Convert a legacy survey to Surveys 2.0 (published as version 1) and move its answer tickets into
survey responses. Idempotent. Up to 1000 tickets move in the request; the rest continue in the
background. Returns the outbound (with survey) and migration: { status: 'done'|'running', responses?, warnings? }; 422 { errors } when the legacy form cannot be converted.
Bearer <token>.Ok