Reapply "Add missing admin action files and navigation links"

This reverts commit 4d515bc400.

src/app/admin/import/furni/loading.tsx

@@ -0,0 +1,21 @@
+import { Skeleton } from '@/components/ui/skeleton'
+
+export default function ImportFurniLoading() {
+  return (
+    <div className="space-y-6">
+      <div>
+        <Skeleton className="h-9 w-48" />
+        <Skeleton className="h-5 w-72 mt-2" />
+      </div>
+      <div className="rounded-lg border bg-card p-6 space-y-4">
+        {Array.from({ length: 6 }).map((_, i) => (
+          <div key={i} className="space-y-2">
+            <Skeleton className="h-4 w-24" />
+            <Skeleton className="h-10 w-full" />
+          </div>
+        ))}
+        <Skeleton className="h-10 w-24 mt-4" />
+      </div>
+    </div>
+  )
+}