feat: implement clipboard utility for copying text and update components to use it

frontend/app/files/[token]/CopyLinkButton.tsx

@@ -1,6 +1,7 @@
 "use client";
 
 import { useState } from "react";
+import { copyText } from "@/lib/clipboard";
 
 export default function CopyLinkButton({ token }: { token: string }) {
   const [copied, setCopied] = useState(false);
@@ -8,21 +9,11 @@ export default function CopyLinkButton({ token }: { token: string }) {
   async function copy() {
     const url = `${window.location.origin}/files/${token}`;
     try {
-      await navigator.clipboard.writeText(url);
+      await copyText(url);
       setCopied(true);
       setTimeout(() => setCopied(false), 2500);
     } catch {
-      // Fallback for browsers that deny clipboard access
-      const el = document.createElement("textarea");
-      el.value = url;
-      el.style.position = "fixed";
-      el.style.opacity = "0";
-      document.body.appendChild(el);
-      el.select();
-      document.execCommand("copy");
-      document.body.removeChild(el);
-      setCopied(true);
-      setTimeout(() => setCopied(false), 2500);
+      // copy completely unavailable (e.g. sandboxed iframe) — do nothing
     }
   }