feat: add hidden /portal page for SinoCode iframe embedding

Full-screen landing page with glassmorphism cards linking to monitoring
(8018), docs (8017), and analytics (8019). Sidebar is conditionally
hidden on the portal route. Supports dark/light themes and i18n.

components/ClientProviders.tsx

@@ -1,16 +1,26 @@
 "use client";
 
 import { type ReactNode } from "react";
+import { usePathname } from "next/navigation";
 import { I18nProvider } from "@/lib/i18n";
 import { ThemeProvider } from "@/lib/theme";
 import { Sidebar } from "@/components/Sidebar";
 
 export function ClientProviders({ children }: { children: ReactNode }) {
+  const pathname = usePathname();
+  const isPortal = pathname === "/portal";
+
   return (
     <ThemeProvider>
       <I18nProvider>
-        <Sidebar />
-        <main className="ml-[220px] min-h-screen p-6 lg:p-8">{children}</main>
+        {isPortal ? (
+          <>{children}</>
+        ) : (
+          <>
+            <Sidebar />
+            <main className="ml-[220px] min-h-screen p-6 lg:p-8">{children}</main>
+          </>
+        )}
       </I18nProvider>
     </ThemeProvider>
   );