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/en.json

@@ -1196,6 +1196,8 @@
       "total": "Total",
       "sent": "Sent",
       "failed": "Failed",
+      "blocked": "Blocked",
+      "blockedShort": "blocked",
       "filter": "Filter",
       "message": "Message",
       "unknownAdmin": "Unknown",