fix(admin): secure routes, add real IP detection, SMTP header validation, and fix Next.js layout hydration mismatch

frontend/src/app/admin/layout.tsx

@@ -20,8 +20,10 @@ export default function AdminLayout({
   const [isChecking, setIsChecking] = useState(true);
   const [isValid, setIsValid] = useState(false);
   const [persistHydrated, setPersistHydrated] = useState(false);
+  const [isMounted, setIsMounted] = useState(false);
 
   useEffect(() => {
+    setIsMounted(true);
     const unsub = useTranslationStore.persist.onFinishHydration(() => {
       setPersistHydrated(true);
     });
@@ -31,6 +33,10 @@ export default function AdminLayout({
     return unsub;
   }, []);
 
+  if (!isMounted) {
+    return null;
+  }
+
   const verifyToken = useCallback(async (token: string): Promise<boolean> => {
     try {
       const response = await fetch(`${API_BASE}/api/v1/admin/verify`, {