fix(format): convert price by exchange rate on landings and gift page

formatPrice from utils/format.ts only swapped the currency symbol
(220 ₽ -> ¥220) without converting the underlying amount, because it
had no source of exchange rates and the landing/gift pages never called
the useCurrency hook that knew how to fetch them.

- Add a module-level rates cache in utils/format with setExchangeRates
  setter. formatPrice now converts kopeks/100 from RUB to the target
  currency via currencyApi.convertFromRub when rates are cached.
- useCurrency pushes its loaded rates into that cache so any subsequent
  formatPrice call benefits, including subcomponents that cannot easily
  receive a prop.
- Call useCurrency in QuickPurchase, GiftSubscription, and
  AdminLandingEditor — the only entry points whose subcomponents still
  use the synchronous formatPrice (everything else already routes
  through useCurrency.formatAmount).

For RU locale behavior is unchanged. For EN/ZH/FA the amount is now
divided by the per-currency rate and formatted via Intl.NumberFormat
with 2 fraction digits (0 for IRR since amounts are large).

src/pages/GiftSubscription.tsx

@@ -19,6 +19,7 @@ import { cn } from '../lib/utils';
 import { copyToClipboard } from '../utils/clipboard';
 import { getApiErrorMessage } from '../utils/api-error';
 import { formatPrice } from '../utils/format';
+import { useCurrency } from '../hooks/useCurrency';
 import { usePlatform, useHaptic } from '@/platform';
 
 function GiftIcon({ className }: { className?: string }) {
@@ -1286,6 +1287,9 @@ export default function GiftSubscription() {
   const { t } = useTranslation();
   const [searchParams] = useSearchParams();
 
+  // Прогреваем кэш курсов валют для formatPrice (см. QuickPurchase).
+  useCurrency();
+
   // URL params: ?tab=activate&code=TOKEN for auto-activation
   const urlTab = searchParams.get('tab') as TabId | null;
   const rawCode = searchParams.get('code');