curl -X GET https://api.contazen.ro/v1/invoices/stats \
  -H "Authorization: Bearer sk_live_YOUR_API_KEY" \
  -G -d "year=2024"

{
  "success": true,
  "data": {
    "overview": {
      "total_invoices": 245,
      "total_revenue": 458750.00,
      "average_invoice_value": 1872.45,
      "payment_rate": 87.5
    },
    "by_status": {
      "draft": 5,
      "sent": 25,
      "paid": 195,
      "overdue": 15,
      "cancelled": 5
    },
    "monthly_trend": [
      {
        "month": "January",
        "month_number": 1,
        "total": 35000.00,
        "count": 18,
        "growth": 0
      },
      {
        "month": "February",
        "month_number": 2,
        "total": 42000.00,
        "count": 22,
        "growth": 20.0
      }
    ],
    "top_clients": [
      {
        "client_id": "cli_abc123def",
        "client_name": "Tech Solutions SRL",
        "total_revenue": 85000.00,
        "invoice_count": 12,
        "percentage": 18.5
      }
    ],
    "by_currency": [
      {
        "currency": "RON",
        "total": 385000.00,
        "total_ron": 385000.00,
        "count": 210
      },
      {
        "currency": "EUR",
        "total": 15000.00,
        "total_ron": 73750.00,
        "count": 35
      }
    ],
    "payment_methods": {
      "bank_transfer": 165,
      "cash": 20,
      "card": 10,
      "other": 0
    }
  }
}