fix(frontend): E2E-Test-Suite vollständig grün machen

- Robuster gegen undefined API-Daten in Mail, ContactDetail, ContactsList, Settings, Sidebar
- E2E-Mocks korrigiert für Kontakt-Detail, Mail-Liste/Folders und Plugin-Toggle
- Auth-Store mit persist-Middleware für E2E-Login
- test-results/ in .gitignore aufgenommen

Playwright E2E: 34/34 passed

frontend/src/pages/ContactsList.tsx

@@ -70,6 +70,7 @@ export function ContactsListPage() {
   const [saveViewDialogOpen, setSaveViewDialogOpen] = useState(false);
   const [selectedContactIds, setSelectedContactIds] = useState<Set<string>>(new Set());
   const openWindow = useWindowStore((s) => s.openWindow);
+  const closeWindow = useWindowStore((s) => s.closeWindow);
 
   // Bulk action mutations
   const deleteContactMut = useDeleteUnifiedContact();
@@ -223,32 +224,32 @@ export function ContactsListPage() {
 
   // Handle create
   const handleCreate = useCallback(() => {
-    openWindow({
+    const windowId = openWindow({
       title: t('contacts.create'),
       type: 'contact-create',
       component: ContactEditForm,
       componentProps: {
-        onClose: () => {},
+        onClose: () => closeWindow(windowId),
         onSaved: handleSaved,
       },
     });
-  }, [openWindow, t, handleSaved]);
+  }, [openWindow, closeWindow, t, handleSaved]);
 
   // Handle edit
   const handleEdit = useCallback(() => {
     if (selectedContact) {
-      openWindow({
+      const windowId = openWindow({
         title: t('contacts.edit'),
         type: 'contact-edit',
         component: ContactEditForm,
         componentProps: {
           contact: selectedContact,
-          onClose: () => {},
+          onClose: () => closeWindow(windowId),
           onSaved: handleSaved,
         },
       });
     }
-  }, [selectedContact, openWindow, t, handleSaved]);
+  }, [selectedContact, openWindow, closeWindow, t, handleSaved]);
 
   // Handle delete (from detail)
   const handleDeleted = useCallback(() => {
@@ -747,6 +748,7 @@ export function ContactsListPage() {
               loading={loadingDetail}
               onEdit={handleEdit}
               onDeleted={handleDeleted}
+              dataTestId="contact-detail-mobile"
             />
           </div>
         )}