fix: update layout.tsx to import Viewport type and restructure viewport definition

Author: Marvin Zhang

docs-site

@@ -1,4 +1,4 @@
-import type { Metadata } from "next";
+import type { Metadata, Viewport } from "next";
 import "./globals.css";
 import { Navigation } from "@/components/navigation";
 import { MainSidebar } from "@/components/main-sidebar";
@@ -21,11 +21,12 @@ export const metadata: Metadata = {
     description: "Browse and explore LeanSpec specifications in a rich, interactive format",
     type: "website",
   },
-  viewport: {
-    width: 'device-width',
-    initialScale: 1,
-    maximumScale: 5,
-  },
+};
+
+export const viewport: Viewport = {
+  width: 'device-width',
+  initialScale: 1,
+  maximumScale: 5,
 };
 
 export default async function RootLayout({