feat(layout): add ProblemDescriptionLayout component for structured layout

src/app/(app)/playground/@problem/@description/layout.tsx

@@ -0,0 +1,13 @@
+interface ProblemDescriptionLayoutProps {
+  children: React.ReactNode;
+}
+
+export default function ProblemDescriptionLayout({
+  children,
+}: ProblemDescriptionLayoutProps) {
+  return (
+    <div className="h-full flex flex-col">
+      {children}
+    </div>
+  );
+}