curl -X GET "https://app.tracia.io/api/v1/spans?promptSlug=welcome-email&limit=20" \
  -H "Authorization: Bearer tr_your_api_key"

const { spans, nextCursor } = await tracia.spans.list({
  promptSlug: 'welcome-email',
  limit: 20
});

{
  "spans": [
    {
      "id": "clx1abc123",
      "spanId": "sp_abc123def456",
      "traceId": "tr_session123",
      "promptSlug": "welcome-email",
      "model": "gpt-4o",
      "status": "SUCCESS",
      "latencyMs": 1250,
      "inputTokens": 150,
      "outputTokens": 320,
      "totalTokens": 470,
      "cost": 0.0234,
      "createdAt": "2024-01-15T10:30:00.000Z"
    }
  ],
  "nextCursor": "clx2def456"
}

{
  "error": {
    "code": "UNAUTHORIZED",
    "message": "Invalid or missing API key"
  }
}