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/QuickPurchase.tsx

@@ -19,6 +19,7 @@ import LanguageSwitcher from '../components/LanguageSwitcher';
 import { cn } from '../lib/utils';
 import { getApiErrorMessage } from '../utils/api-error';
 import { formatPrice } from '../utils/format';
+import { useCurrency } from '../hooks/useCurrency';
 
 function detectContactType(value: string): 'email' | 'telegram' {
   return value.startsWith('@') ? 'telegram' : 'email';
@@ -795,6 +796,10 @@ export default function QuickPurchase() {
   const { t, i18n } = useTranslation();
   const queryClient = useQueryClient();
 
+  // Подгружаем курсы валют, чтобы formatPrice конвертировал суммы для не-RU локалей
+  // (хук кладёт rates в глобальный кэш utils/format.ts).
+  useCurrency();
+
   // Fetch config
   const {
     data: config,