Add Seller Member

curl -X POST 'http://localhost:9000/admin/sellers/sel_01HXYZABCDEF/members' \
  -H 'Authorization: Bearer <token>' \
  -H 'Content-Type: application/json' \
  -d '{"member_id": "mem_01HXYZMEMBB", "role_id": "role_01HXYZROLEAA"}'

const { seller_member } = await client.admin.sellers.$id.members.mutate({
  $id: "sel_01HXYZABCDEF",
  member_id: "mem_01HXYZMEMBB",
  role_id: "role_01HXYZROLEAA",
})

{
  "seller_member": {
    "id": "selmem_01HXYZSMBB",
    "seller_id": "sel_01HXYZABCDEF",
    "member_id": "mem_01HXYZMEMBB",
    "is_owner": false,
    "created_at": "2026-06-15T09:00:00.000Z"
  }
}