Brakeman fix:
- users_controller: :role only permitted for admin/superadmin
  (prevents privilege escalation via mass assignment)

German locale (de.yml):
- Complete translation (~300 keys) matching ru.yml/en.yml coverage
- All navigation, tickets, invoices, chat, settings, AI, notifications,
  knowledge, price lists, auth, errors, a11y
- Now all 3 languages fully supported without "translation missing"