feat: fetch exchange rates immediately on startup

Start fetching exchange rates immediately upon initialization, ensuring the most current data is available from the outset. This prevents potential inaccuracies during initial use if rates are only fetched after the interval delay.

src/js/main.js

@@ -62,7 +62,8 @@ document.addEventListener('DOMContentLoaded', function () {
     }
   });
 
-  // Fetch updated exchange rates every 5 seconds
+  // Fetch updated exchange rates immediately, then every 5 seconds
+  fetchUpdatedExchangeRates();
   setInterval(fetchUpdatedExchangeRates, 5000);
 });