Add 404 Not Found page component and update routing and sitemap configuration

src/App.js

@@ -40,6 +40,7 @@ const ServerLogsPage = lazy(() => import(/* webpackChunkName: "admin-logs" */ ".
 // Lazy load legal pages - rarely accessed
 const Datenschutz = lazy(() => import(/* webpackChunkName: "legal" */ "./pages/Datenschutz.js"));
 const AGB = lazy(() => import(/* webpackChunkName: "legal" */ "./pages/AGB.js"));
+const NotFound404 = lazy(() => import(/* webpackChunkName: "legal" */ "./pages/NotFound404.js"));
 const Sitemap = lazy(() => import(/* webpackChunkName: "sitemap" */ "./pages/Sitemap.js"));
 const Impressum = lazy(() => import(/* webpackChunkName: "legal" */ "./pages/Impressum.js"));
 const Batteriegesetzhinweise = lazy(() => import(/* webpackChunkName: "legal" */ "./pages/Batteriegesetzhinweise.js"));
@@ -232,6 +233,7 @@ const AppContent = ({ currentTheme, onThemeChange }) => {
             {/* Legal pages */}
             <Route path="/datenschutz" element={<Datenschutz />} />
             <Route path="/agb" element={<AGB />} />
+            <Route path="/404" element={<NotFound404 />} />
             <Route path="/sitemap" element={<Sitemap />} />
             <Route path="/impressum" element={<Impressum />} />
             <Route

src/pages/NotFound404.js

@@ -0,0 +1,17 @@
+import React from 'react';
+import { Typography } from '@mui/material';
+import LegalPage from './LegalPage.js';
+
+const NotFound404 = () => {
+  const content = (
+    <>
+      <Typography variant="body1" paragraph>
+        This page is no longer available.
+      </Typography>
+    </>
+  );
+
+  return <LegalPage title="Page Not Found" content={content} />;
+};
+
+export default NotFound404;