- 7 API endpoints: GET /contacts (list+search+filter+sort+paginate), POST /contacts (create), GET /contacts/:id (detail+persons), PUT /contacts/:id (update), DELETE /contacts/:id (soft-delete), POST /contacts/:id/persons (add person), DELETE /contacts/:id/persons/:pid (remove person)
- Contact service: list_contacts (search, role filter with beide inclusion, is_eu filter, is_private filter, sort, pagination), get_contact_by_id, create_contact (with nested persons), update_contact, soft_delete_contact, add_contact_person, remove_contact_person
- USt-IdNr. validation: DE + 10 EU countries regex patterns, EU fallback, validate_vat_id, validate_vat_id_or_raise, get_country_code_from_vat_id
- RBAC: all roles read, admin+verkaeufer write (require_role dependency)