fix: remove inline script and improve noscript message

Refactored inline exchangeRates script to main.js for better practice and maintainability. Enhanced the noscript warning message's readability by replacing paragraph tags with line breaks, ensuring clearer instructions for users without JavaScript.

src/js/main.js

@@ -14,6 +14,8 @@ console.log(tooltipList);
 
 let lastModifiedField = 'xmr';
 
+var exchangeRates = {};
+
 document.addEventListener('DOMContentLoaded', function () {
   const copyXMRBtn = document.getElementById('copyXMRBtn');
   const copyFiatBtn = document.getElementById('copyFiatBtn');