fixed back button with source, and customer in customer lsit clickable

frontend/src/pages/contracts/ContractForm.tsx

@@ -1,5 +1,5 @@
 import { useEffect, useState } from 'react';
-import { useNavigate, useParams, useSearchParams } from 'react-router-dom';
+import { useNavigate, useParams, useSearchParams, useLocation } from 'react-router-dom';
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { useForm } from 'react-hook-form';
 import { contractApi, customerApi, platformApi, cancellationPeriodApi, contractDurationApi, providerApi, contractCategoryApi } from '../../services/api';
@@ -61,8 +61,10 @@ export default function ContractForm() {
   const { id } = useParams();
   const [searchParams] = useSearchParams();
   const navigate = useNavigate();
+  const location = useLocation();
   const queryClient = useQueryClient();
   const isEdit = !!id;
+  const backTo = (location.state as any)?.from as string | undefined;
 
   const preselectedCustomerId = searchParams.get('customerId');
 
@@ -656,7 +658,7 @@ export default function ContractForm() {
   return (
     <div>
       <div className="flex items-center gap-4 mb-6">
-        <Button variant="ghost" size="sm" onClick={() => navigate(isEdit ? `/contracts/${id}` : '/contracts')}>
+        <Button variant="ghost" size="sm" onClick={() => navigate(backTo || (isEdit ? `/contracts/${id}` : '/contracts'))}>
           <ArrowLeft className="w-4 h-4" />
         </Button>
         <h1 className="text-2xl font-bold">
@@ -1407,7 +1409,7 @@ export default function ContractForm() {
         </Card>
 
         <div className="flex justify-end gap-4">
-          <Button type="button" variant="secondary" onClick={() => navigate(isEdit ? `/contracts/${id}` : '/contracts')}>
+          <Button type="button" variant="secondary" onClick={() => navigate(backTo || (isEdit ? `/contracts/${id}` : '/contracts'))}>
             Abbrechen
           </Button>
           <Button type="submit" disabled={isLoading}>