fix: complete is_limited status handling across all views

- SubscriptionListCard: show traffic progress bar for limited subs
  in multi-tariff list (was hidden because isActive excluded limited)
- SubscriptionListCard: amber border/background for limited status
  cards (was using default neutral style, inconsistent with rest of UI)
- Subscription page: hide delete button for limited subs in
  multi-tariff mode (limited subs still have valid days remaining)
- SubscriptionPurchase: allow tariff switch for limited subs
  (was blocked by is_active-only gate in canSwitch formula)
- AdminUserDetail: include limited status in "already purchased"
  tariff filter to prevent duplicate subscription creation

src/pages/SubscriptionPurchase.tsx

@@ -781,7 +781,7 @@ export default function SubscriptionPurchase() {
                       !isCurrentTariff &&
                       !subscription.is_trial &&
                       !isSubscriptionExpired &&
-                      subscription.is_active;
+                      (subscription.is_active || subscription.is_limited);
                     const isLegacySubscription =
                       subscription && !subscription.is_trial && !subscription.tariff_id;