fix: remove nonexistent MainLayout wrapper from Buchhaltung page

frontend/src/pages/Buchhaltung.tsx

@@ -41,7 +41,6 @@ import {
 } from '@mui/icons-material';
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { useLocation, useNavigate } from 'react-router-dom';
-import MainLayout from '../components/shared/MainLayout';
 import { buchhaltungApi } from '../services/buchhaltung';
 import { useNotification } from '../contexts/NotificationContext';
 import { usePermissionContext } from '../contexts/PermissionContext';
@@ -807,8 +806,7 @@ export default function Buchhaltung() {
   };
 
   return (
-    <MainLayout>
-      <Box sx={{ p: 3 }}>
+    <Box sx={{ p: 3 }}>
         <Box sx={{ display: 'flex', alignItems: 'center', mb: 3, gap: 2 }}>
           <Typography variant="h4" fontWeight={700}>Buchhaltung</Typography>
         </Box>
@@ -840,7 +838,6 @@ export default function Buchhaltung() {
             onJahrChange={setSelectedJahrId}
           />
         )}
-      </Box>
-    </MainLayout>
+    </Box>
   );
 }