curl -X GET "https://olive-gateway-a6ba.onrender.com/api/v1/subscribers/sub_abc123/cards" \
  -H "Authorization: Bearer olive_live_xxx"

{
  "cards": [
    {
      "serial": "OLIV0001",
      "type": "PARENT",
      "status": "ACTIVE",
      "mac_address": "AA:BB:CC:DD:EE:01",
      "linked_at": "2025-01-15T10:30:00Z"
    },
    {
      "serial": "OLIV0002",
      "type": "CHILD",
      "status": "ACTIVE",
      "mac_address": "AA:BB:CC:DD:EE:02",
      "daily_limit": 50000,
      "parent_serial": "OLIV0001",
      "linked_at": "2025-01-16T14:00:00Z"
    }
  ],
  "count": 2
}