feat: show blocked_count in broadcast admin UI

- Add blocked_count to Broadcast interface
- 4-column stats grid with blocked card (warning color)
- Show blocked count in broadcast list when > 0
- Fetch single broadcast by ID instead of listing all
- Add i18n keys for blocked/blockedShort in ru/en/zh/fa

src/locales/ru.json

@@ -1221,6 +1221,8 @@
       "total": "Всего",
       "sent": "Отправлено",
       "failed": "Ошибки",
+      "blocked": "Заблокировали",
+      "blockedShort": "заблок.",
       "filter": "Фильтр",
       "message": "Сообщение",
       "unknownAdmin": "Неизвестный админ",