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

frontend/src/pages/contracts/ContractDetail.tsx

@@ -1,5 +1,5 @@
 import { useState, useEffect } from 'react';
-import { useParams, Link, useNavigate } from 'react-router-dom';
+import { useParams, Link, useNavigate, useLocation } from 'react-router-dom';
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { contractApi, uploadApi, meterApi, contractTaskApi, appSettingsApi, gdprApi } from '../../services/api';
 import { ContractEmailsSection } from '../../components/email';
@@ -1210,7 +1210,9 @@ function ContractTaskModal({
 export default function ContractDetail() {
   const { id } = useParams();
   const navigate = useNavigate();
+  const location = useLocation();
   const queryClient = useQueryClient();
+  const backTo = (location.state as any)?.from as string | undefined;
   const { hasPermission, isCustomer, isCustomerPortal } = useAuth();
   const contractId = parseInt(id!);
 
@@ -1428,7 +1430,7 @@ export default function ContractDetail() {
     return (
       <div>
         <div className="flex items-center gap-4 mb-6">
-          <Button variant="ghost" size="sm" onClick={() => navigate(isCustomerPortal ? '/contracts' : (c.customer ? `/customers/${c.customer.id}?tab=contracts` : '/contracts'))}>
+          <Button variant="ghost" size="sm" onClick={() => navigate(backTo || (isCustomerPortal ? '/contracts' : (c.customer ? `/customers/${c.customer.id}?tab=contracts` : '/contracts')))}>
             <ArrowLeft className="w-4 h-4" />
           </Button>
           <h1 className="text-2xl font-bold">Vertrag {c.contractNumber}</h1>
@@ -1463,7 +1465,7 @@ export default function ContractDetail() {
             <Button
               variant="ghost"
               size="sm"
-              onClick={() => navigate(isCustomerPortal ? '/contracts' : (c.customer ? `/customers/${c.customer.id}?tab=contracts` : '/contracts'))}
+              onClick={() => navigate(backTo || (isCustomerPortal ? '/contracts' : (c.customer ? `/customers/${c.customer.id}?tab=contracts` : '/contracts')))}
             >
               <ArrowLeft className="w-4 h-4" />
             </Button>
@@ -1497,7 +1499,7 @@ export default function ContractDetail() {
           {c.customer && (
             <p className="text-gray-500 ml-10">
               Kunde:{' '}
-              <Link to={`/customers/${c.customer.id}`} className="text-blue-600 hover:underline">
+              <Link to={`/customers/${c.customer.id}`} state={{ from: `/contracts/${id}` }} className="text-blue-600 hover:underline">
                 {c.customer.companyName || `${c.customer.firstName} ${c.customer.lastName}`}
               </Link>
             </p>
@@ -1532,7 +1534,7 @@ export default function ContractDetail() {
               </Link>
             )}
             {hasPermission('contracts:update') && (
-              <Link to={`/contracts/${id}/edit`}>
+              <Link to={`/contracts/${id}/edit`} state={{ from: `/contracts/${id}` }}>
                 <Button variant="secondary">
                   <Edit className="w-4 h-4 mr-2" />
                   Bearbeiten