Add duplicate link action with unique name prefill

frontend/src/app.tsx

@@ -361,6 +361,27 @@ function AdminPage({
     });
   };
 
+  const startDuplicate = (link: LinkItem) => {
+    const existingNames = new Set(orderedLinks.map((item) => item.name.toLowerCase()));
+    const base = `${link.name} (copy)`;
+    let candidate = base;
+    let counter = 2;
+    while (existingNames.has(candidate.toLowerCase())) {
+      candidate = `${base} ${counter}`;
+      counter += 1;
+    }
+    setEditingId(null);
+    setFile(null);
+    setForm({
+      name: candidate,
+      url: link.url,
+      description: link.description,
+      category: link.category,
+      icon_url: link.icon_url ?? '',
+      enabled: link.enabled,
+    });
+  };
+
   const reset = () => {
     setEditingId(null);
     setFile(null);
@@ -511,6 +532,7 @@ function AdminPage({
               <div className="flex gap-2">
                 <button type="button" className="btn-subtle" onClick={() => moveBy(link.id, -1)} disabled={index === 0}>Up</button>
                 <button type="button" className="btn-subtle" onClick={() => moveBy(link.id, 1)} disabled={index === orderedLinks.length - 1}>Down</button>
+                <button type="button" className="btn-subtle" onClick={() => startDuplicate(link)}>Duplicate</button>
                 <button type="button" className="btn-subtle" onClick={() => startEdit(link)}>Edit</button>
                 <button type="button" className="btn-subtle" onClick={() => onDelete(link.id)}>Delete</button>
               </div>