fix: update DOI URL to use freedoi.org

Replaces the dynamic origin-based DOI URL with a standardized URL using freedoi.org. This ensures consistent and accurate DOI links, improving user experience and reliability.

assets/js/clipboard.js

@@ -5,7 +5,7 @@ document.addEventListener("DOMContentLoaded", function () {
   doiLink.addEventListener("click", function (event) {
     event.preventDefault();
     const doi = doiLink.getAttribute("data-doi");
-    const fullDoiUrl = `${window.location.origin}/${doi}`;
+    const fullDoiUrl = `https://freedoi.org/${doi}`;
 
     navigator.clipboard.writeText(fullDoiUrl).then(
       function () {