feat: archived-Feld in Kunden-Admin-API durchreichen

sanitizeCustomer liefert jetzt customers.archived, damit das Ticketsystem den
Archiviert-Status ueber /api/admin/customers erhaelt.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/services/customerAdmin.js

@@ -39,6 +39,7 @@ function sanitizeCustomer(customer, { portalPassword } = {}) {
     portalAccessEnabled: Boolean(customer.portalAccessEnabled),
     appwriteUserId: customer.appwriteUserId || '',
     customerStatus: customer.customerStatus || '',
+    archived: Boolean(customer.archived),
     portalPassword: storedPassword || '',
   }
 }