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/hooks/useCurrency.ts

@@ -1,7 +1,8 @@
-import { useCallback, useMemo } from 'react';
+import { useCallback, useEffect, useMemo } from 'react';
 import { useQuery } from '@tanstack/react-query';
 import { useTranslation } from 'react-i18next';
 import { currencyApi, type ExchangeRates } from '../api/currency';
+import { setExchangeRates as setGlobalExchangeRates } from '../utils/format';
 
 // Map language to currency
 const LANGUAGE_CURRENCY_MAP: Record<string, keyof ExchangeRates | 'RUB'> = {
@@ -30,6 +31,12 @@ export function useCurrency() {
     retry: 2,
   });
 
+  // Делимся курсом с синхронным formatPrice из utils/format.ts —
+  // у него нет своего источника rates, а на лендинге его дёргают subcomponents.
+  useEffect(() => {
+    setGlobalExchangeRates(exchangeRates);
+  }, [exchangeRates]);
+
   // Get current language and currency
   const currentLanguage = i18n.language;
   const targetCurrency = LANGUAGE_CURRENCY_MAP[currentLanguage] || 'USD';