Update Tier

curl -X PUT "https://api.clustr-ai.com/api/public/tenant-tiers/1a2b3c4d-..." \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"position": 0}'

{
  "success": true,
  "data": { "id": "1a2b3c4d-...", "name": "Strategic", "position": 0 }
}

{
  "success": false,
  "error": { "message": "tier not found", "code": "NOT_FOUND" }
}