curl --location '/plans/' \
--header 'Authorization: Bearer <token>'{
"plan_id": "string",
"title": "제주도 겨울 여행",
"thumbnail": "string",
"start_date": "2026-01-04",
"end_date": "2026-01-08",
"duration_days": 0,
"member_count": 0,
"collection_count": 0
}