13. Kalkulator walutowy

// Darmowe API: https://api.exchangerate-api.com/v4/latest/PLN
// lub: https://api.frankfurter.app/latest?base=PLN&symbols=USD,EUR,GBP

async function getRates(baseCurrency = 'PLN') {
  const res = await fetch(`https://api.frankfurter.app/latest?base=${baseCurrency}`);
  const data = await res.json();
  return data.rates; // { USD: 0.25, EUR: 0.23, ... }
}