feat: add Studio loading skeleton

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

app/(app)/studio/loading.tsx

@@ -0,0 +1,16 @@
+export default function StudioLoading() {
+  return (
+    <div className="p-6 space-y-8 animate-pulse">
+      <div>
+        <div className="h-8 w-24 bg-gray-200 rounded" />
+        <div className="h-4 w-64 bg-gray-100 rounded mt-2" />
+      </div>
+      <div className="rounded-2xl h-24 bg-gray-200" />
+      <div className="space-y-2">
+        {[...Array(6)].map((_, i) => (
+          <div key={i} className="h-12 bg-gray-100 rounded-xl" />
+        ))}
+      </div>
+    </div>
+  )
+}