feat: implement layout 3-tier container architecture, desktop screen token, Gate 8 no-escape rule, and clean dead code

refer_landing_page/app/layout.tsx

@@ -45,7 +45,7 @@ export default function RootLayout({
       </head>
       <body className="flex min-h-screen flex-col">
         <Header />
-        <main className="flex-1">{children}</main>
+        <main className="w-full flex-1">{children}</main>
         <Footer />
       </body>
     </html>