fix: limited (traffic exhausted) subscription shows as expired

- Dashboard card: change date label from "Истекла" to "Активна до"
  for limited subscriptions (traffic exhausted but time remaining)
- Dashboard button: change text from "Трафик исчерпан" (dead-end) to
  "Докупить трафик" (actionable) for limited status
- Subscription page: CountdownTimer shows remaining time for limited
  subs instead of "Истекла" (was passing is_active=false)
- PurchaseCTAButton: don't treat limited as expired — limited subs
  still have time, should show extend CTA not "buy new subscription"

src/locales/en.json

@@ -272,7 +272,8 @@
       "tariffs": "Tariffs",
       "traffic": "Traffic",
       "devices": "Devices",
-      "expiredDate": "Expired"
+      "expiredDate": "Expired",
+      "activeUntil": "Active until"
     },
     "suspended": {
       "title": "Subscription Suspended",