feat: real back-in-stock subscription for Notify Me (API + localStorage fallback)

notifyMe() just called toggleWishlist() - no actual subscription
mechanism existed. Now calls a new subscribeToRestock() API method
(POST /items/{id}/notify-me, not yet built server-side - see
BACKEND-API-REFERENCE.md §12.5) and falls back to a local-only record
in localStorage on failure, so the request isn't silently dropped
while the backend catches up.

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

src/app/i18n/ru.ts

@@ -321,6 +321,7 @@ export const ru: Translations = {
     compare: 'Сравнить',
     share: 'Поделиться',
     notifyMe: 'Сообщить о наличии',
+    notifyMeConfirmed: 'Мы сообщим вам, когда товар снова появится в наличии.',
     zoom: 'Увеличить',
     fullscreen: 'Полный экран',
     pdfDocument: 'PDF документ товара',