Create contact group

curl -X POST 'https://api.sndr.sh/v1/contact-groups' \
  -H "Authorization: Bearer $SNDR_API_KEY" \
  -H 'Content-Type: application/json' \
  -d '{"name": "VIP customers", "description": "Accounts over $10k ARR"}'

{
  "id":              "grp_4d8a0c5e-1f7",
  "organization_id": "org_8d41c7a2-3f6",
  "name":            "VIP customers",
  "slug":            "vip-customers",
  "description":     "Accounts over $10k ARR",
  "member_count":    0,
  "created_at":      "2026-06-01T12:00:00Z"
}