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/components/dashboard/SubscriptionCardExpired.tsx

@@ -228,7 +228,7 @@ export default function SubscriptionCardExpired({
       >
         <div className="flex items-center">
           <div className="mb-0.5 font-mono text-[10px] font-medium uppercase tracking-wider text-dark-50/30">
-            {t('dashboard.expired.expiredDate')}
+            {isLimited ? t('dashboard.expired.activeUntil') : t('dashboard.expired.expiredDate')}
           </div>
           <div className="ml-3 text-base font-bold tracking-tight text-dark-50/50">
             {formattedDate}
@@ -280,7 +280,7 @@ export default function SubscriptionCardExpired({
             >
               <path d="M12 4.5v15m7.5-7.5h-15" />
             </svg>
-            {t('subscription.trafficLimited')}
+            {t('subscription.buyTraffic')}
           </Link>
         ) : (
           <>