feat: add readyState check

Author: wsafight

src/components/misc/Markdown.astro

@@ -17,8 +17,10 @@ const className = Astro.props.class
   const observer = new MutationObserver(addPreCopyButton);
   observer.observe(document.body, { childList: true, subtree: true });
 
-  document.addEventListener("DOMContentLoaded", addPreCopyButton);
-
+  if (document.readyState === "loading") {
+    document.addEventListener("DOMContentLoaded", addPreCopyButton);
+  }
+  
   function addPreCopyButton() {
     observer.disconnect();