feat(legal): wire recurrent-payments document + restore footer link

Backend now serves a dedicated recurring-payments legal document, so:
- Add adminLegalPagesApi.get/updateRecurrentPayments and infoApi.getRecurrentPayments
  (+ InfoVisibility.recurrent).
- AdminLegalPages: new 'Рекуррентные платежи' editor tab (DocumentEditor now driven
  by a DOCUMENT_API dispatch map instead of privacy/offer ternaries).
- PublicLegal: add 'recurrent' doc; add public /recurrent-payments route.
- Re-add the recurrent link to the login LegalFooter (was removed pending backend).
- i18n: admin.legalPages.tabs.recurrent for ru/en/fa/zh (footer.recurrent already existed).

type-check, eslint, prettier and build all pass.

src/components/LegalFooter.tsx

@@ -7,12 +7,10 @@ interface LegalLink {
   fallback: string;
 }
 
-// Recurring-payments has no dedicated legal document in the backend yet, so it is
-// intentionally omitted rather than pointed at unrelated content. Re-add once a
-// `recurrent-payments` document + public endpoint exist.
 const LINKS: LegalLink[] = [
   { href: '/offer', labelKey: 'footer.offer', fallback: 'Публичная оферта' },
   { href: '/privacy', labelKey: 'footer.privacy', fallback: 'Политика конфиденциальности' },
+  { href: '/recurrent-payments', labelKey: 'footer.recurrent', fallback: 'Рекуррентные платежи' },
 ];
 
 interface LegalFooterProps {