feat: implement user authentication and admin management

- Add user management API endpoints for listing and creating users.
- Implement login and logout functionality with rate limiting.
- Create UI components for login form, logout button, and animated elements.
- Add session management with JWT and secure cookie handling.
- Seed initial admin user if no users exist.
- Introduce utility functions for password hashing and user authentication.
- Set up proxy middleware for route protection and security headers.
- Create a JSON file for user data storage.
- Add links configuration for external resources.

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

@@ -1,18 +1,55 @@
 "use client";
 
+import { useState } from "react";
+
 export default function CopyLinkButton({ token }: { token: string }) {
-  function copy() {
+  const [copied, setCopied] = useState(false);
+
+  async function copy() {
     const url = `${window.location.origin}/files/${token}`;
-    navigator.clipboard.writeText(url).then(() => {
-      alert("Link copied to clipboard!");
-    });
+    try {
+      await navigator.clipboard.writeText(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);
+    }
   }
+
   return (
     <button
       onClick={copy}
-      className="flex w-full items-center justify-center gap-2 rounded-xl border border-slate-700 py-3 text-sm font-semibold text-slate-300 hover:bg-slate-800 hover:text-white transition-colors"
+      className={`flex w-full items-center justify-center gap-2.5 rounded-xl border py-3 text-sm font-semibold transition-all ${
+        copied
+          ? "border-emerald-500/40 bg-emerald-500/8 text-emerald-400"
+          : "border-white/8 bg-white/3 text-slate-300 hover:bg-white/6 hover:border-white/16 hover:text-white"
+      }`}
     >
-      Copy share link
+      {copied ? (
+        <>
+          <svg viewBox="0 0 24 24" className="w-4 h-4" fill="none" stroke="currentColor" strokeWidth="2.5" aria-hidden="true">
+            <path strokeLinecap="round" strokeLinejoin="round" d="M4.5 12.75l6 6 9-13.5" />
+          </svg>
+          Link copied!
+        </>
+      ) : (
+        <>
+          <svg viewBox="0 0 24 24" className="w-4 h-4" fill="none" stroke="currentColor" strokeWidth="2" aria-hidden="true">
+            <path strokeLinecap="round" strokeLinejoin="round" d="M13.19 8.688a4.5 4.5 0 011.242 7.244l-4.5 4.5a4.5 4.5 0 01-6.364-6.364l1.757-1.757m13.35-.622l1.757-1.757a4.5 4.5 0 00-6.364-6.364l-4.5 4.5a4.5 4.5 0 001.242 7.244" />
+          </svg>
+          Copy share link
+        </>
+      )}
     </button>
   );
 }