fixed all back buttons

frontend/src/pages/contracts/ContractForm.tsx

@@ -656,7 +656,7 @@ export default function ContractForm() {
   return (
     <div>
       <div className="flex items-center gap-4 mb-6">
-        <Button variant="ghost" size="sm" onClick={() => navigate(-1)}>
+        <Button variant="ghost" size="sm" onClick={() => navigate(isEdit ? `/contracts/${id}` : '/contracts')}>
           <ArrowLeft className="w-4 h-4" />
         </Button>
         <h1 className="text-2xl font-bold">
@@ -1407,7 +1407,7 @@ export default function ContractForm() {
         </Card>
 
         <div className="flex justify-end gap-4">
-          <Button type="button" variant="secondary" onClick={() => navigate(-1)}>
+          <Button type="button" variant="secondary" onClick={() => navigate(isEdit ? `/contracts/${id}` : '/contracts')}>
             Abbrechen
           </Button>
           <Button type="submit" disabled={isLoading}>