#41 task list --json includes body (consistency with issue list)

SOURCE: swarm friction #7 (verified: task list --json omits body while issue list --json includes it; no task view verb exists). FIX: task list --json includes body (files are the API; list is a thin view of the file, which always had body; zero runtime cost). No new task view verb (gh has none; files are readable). DONE: [{"id":..,"status":..,"title":..,"body":..,"createdAt":..}]; goldens/tests updated.