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/pages/Subscription.tsx

@@ -957,7 +957,7 @@ export default function Subscription() {
               <div className="mb-5">
                 <CountdownTimer
                   endDate={subscription.end_date}
-                  isActive={subscription.is_active}
+                  isActive={subscription.is_active || subscription.is_limited}
                   glassColors={g}
                 />
               </div>