Reapply "Add missing admin action files and navigation links"

This reverts commit 4d515bc400.

src/app/admin/catalog/loading.tsx

@@ -0,0 +1,44 @@
+import { Skeleton } from '@/components/ui/skeleton'
+
+export default function CatalogLoading() {
+  return (
+    <div className="space-y-6">
+      <div className="flex items-center justify-between">
+        <div>
+          <Skeleton className="h-9 w-48" />
+          <Skeleton className="h-5 w-64 mt-2" />
+        </div>
+        <div className="flex items-center gap-2">
+          <Skeleton className="h-10 w-24" />
+          <Skeleton className="h-10 w-28" />
+        </div>
+      </div>
+
+      {/* Tree skeleton */}
+      <div className="rounded-lg border bg-card">
+        <div className="border-b px-4 py-3 flex items-center justify-between">
+          <div className="flex items-center gap-2">
+            <Skeleton className="h-4 w-4" />
+            <Skeleton className="h-4 w-32" />
+            <Skeleton className="h-5 w-16 rounded-full" />
+          </div>
+          <Skeleton className="h-8 w-56" />
+        </div>
+        <div className="p-2 space-y-1">
+          {Array.from({ length: 12 }).map((_, i) => (
+            <div
+              key={i}
+              className="flex items-center gap-2 px-2 py-1.5"
+              style={{ paddingLeft: `${(i % 3) * 20 + 8}px` }}
+            >
+              <Skeleton className="h-5 w-5 shrink-0" />
+              <Skeleton className="h-5 w-5 shrink-0" />
+              <Skeleton className="h-4 flex-1 max-w-48" />
+              <Skeleton className="h-5 w-8 rounded-full" />
+            </div>
+          ))}
+        </div>
+      </div>
+    </div>
+  )
+}