fix(crm): recent-activity email placeholder + customer-dashboard locale dates

- Recent Activity rendered literal {{email}} — the per-row t() call didn't
  pass the email interpolation var. Source it like formatActivityMessage
  (metadata.email ?? actorName).
- Customer 'Deine Galerien' dates rendered en-US ('May','Jun') under a German
  UI because they used raw date-fns format(parseISO(iso),'PP') with no locale.
  Route through useLocalizedDate().format → honours general_date_format + the
  active language.

frontend/src/pages/admin/AdminDashboard.tsx

@@ -276,6 +276,11 @@ export const AdminDashboard: React.FC = () => {
                 const getActivityMessage = (): string => {
                   const params: Record<string, any> = {
                     eventName: activity.eventName || t('common.unknown'),
+                    // Customer/account activity keys (customer_login,
+                    // customer_invitation_*, customer_updated, …) interpolate
+                    // {{email}}; without it the literal placeholder rendered.
+                    // Sourced the same way formatActivityMessage does.
+                    email: activity.metadata?.email || activity.actorName || '',
                     count: activity.metadata?.count || 0,
                     template: activity.metadata?.template_key || '',
                     categoryName: activity.metadata?.category_name || ''

frontend/src/pages/customer/CustomerDashboardPage.tsx

@@ -25,7 +25,7 @@ import { useNavigate } from 'react-router-dom';
 import { Calendar, Clock, Download, ExternalLink, ImageIcon, AlertCircle } from 'lucide-react';
 import { toast } from 'react-toastify';
 import { useTranslation } from 'react-i18next';
-import { format, parseISO } from 'date-fns';
+import { useLocalizedDate } from '../../hooks/useLocalizedDate';
 import { useQuery } from '@tanstack/react-query';
 
 import { Button, Loading } from '../../components/common';
@@ -51,6 +51,10 @@ const DEFAULT_SORT: SortKey = 'newest';
 export const CustomerDashboardPage: React.FC = () => {
   const { t } = useTranslation();
   const navigate = useNavigate();
+  // Localized date formatting — respects general_date_format + the active UI
+  // language. Previously used raw date-fns `format(parseISO(iso),'PP')` with
+  // no locale, so dates rendered en-US ("May", "Jun") under a German UI.
+  const { format: fmtLocalized } = useLocalizedDate();
 
   const { data: events, isLoading, error } = useQuery({
     queryKey: ['customer-events'],
@@ -125,7 +129,7 @@ export const CustomerDashboardPage: React.FC = () => {
 
   const formatDate = (iso: string | null) => {
     if (!iso) return null;
-    try { return format(parseISO(iso), 'PP'); } catch { return null; }
+    try { return fmtLocalized(iso); } catch { return null; }
   };
 
   return (