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

frontend/src/pages/customers/CustomerDetail.tsx

@@ -1,5 +1,5 @@
 import { useState, useEffect } from 'react';
-import { useParams, Link, useNavigate, useSearchParams } from 'react-router-dom';
+import { useParams, Link, useNavigate, useSearchParams, useLocation } from 'react-router-dom';
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { customerApi, addressApi, bankCardApi, documentApi, meterApi, uploadApi, contractApi, stressfreiEmailApi, emailProviderApi, gdprApi, StressfreiEmail, ContractTreeNode } from '../../services/api';
 import { EmailClientTab } from '../../components/email';
@@ -21,6 +21,8 @@ export default function CustomerDetail({ portalCustomerId }: { portalCustomerId?
   const navigate = useNavigate();
   const queryClient = useQueryClient();
   const { hasPermission, isCustomerPortal } = useAuth();
+  const location = useLocation();
+  const backTo = (location.state as any)?.from as string | undefined;
   const [searchParams, setSearchParams] = useSearchParams();
   const customerId = portalCustomerId || parseInt(id!);
   const defaultTab = searchParams.get('tab') || 'addresses';
@@ -202,7 +204,7 @@ export default function CustomerDetail({ portalCustomerId }: { portalCustomerId?
     <div>
       <div className="flex items-center justify-between mb-6">
         <div className="flex items-center gap-3">
-          <Button variant="ghost" size="sm" onClick={() => navigate(isCustomerPortal ? '/' : '/customers')}>
+          <Button variant="ghost" size="sm" onClick={() => navigate(backTo || (isCustomerPortal ? '/' : '/customers'))}>
             <ArrowLeft className="w-4 h-4" />
           </Button>
           <div>
@@ -219,7 +221,7 @@ export default function CustomerDetail({ portalCustomerId }: { portalCustomerId?
         </div>
         <div className="flex gap-2">
           {hasPermission('customers:update') && (
-            <Link to={`/customers/${id}/edit`}>
+            <Link to={`/customers/${id}/edit`} state={{ from: `/customers/${id}` }}>
               <Button variant="secondary">
                 <Edit className="w-4 h-4 mr-2" />
                 Bearbeiten
@@ -1547,7 +1549,7 @@ function ContractsTab({
                 <div className="w-6" /> // Platzhalter für Ausrichtung
               ) : null}
 
-              <Link to={`/contracts/${contract.id}`} className="font-mono flex items-center gap-1 text-blue-600 hover:underline">
+              <Link to={`/contracts/${contract.id}`} state={{ from: `/customers/${customerId}?tab=contracts` }} className="font-mono flex items-center gap-1 text-blue-600 hover:underline">
                 {contract.contractNumber}
                 <CopyButton value={contract.contractNumber} />
               </Link>