curl --request GET \
  --url https://api.faces.sh/v1/billing/usage

{
  "rows": [
    {
      "group_key": "<string>",
      "group_label": "<string>",
      "input_tokens": 123,
      "output_tokens": 123,
      "provider_cost_usd": 123,
      "markup_usd": 123,
      "total_cost_usd": 123,
      "request_count": 123,
      "tokens_saved": 123,
      "usd_saved": 123
    }
  ],
  "totals": {
    "group_key": "<string>",
    "group_label": "<string>",
    "input_tokens": 123,
    "output_tokens": 123,
    "provider_cost_usd": 123,
    "markup_usd": 123,
    "total_cost_usd": 123,
    "request_count": 123,
    "tokens_saved": 123,
    "usd_saved": 123
  }
}