feat: Improve currency exchange rate fetching in BillingManager by adding a primary source from the Central Bank of Russia and a fallback to an alternative API, along with updates to currency formatting for better precision.

frontend/src/BillingManager.jsx

@@ -116,8 +116,28 @@ function BillingManager() {
   const fetchExchangeRates = async () => {
     setRatesLoading(true);
     try {
-      const response = await axios.get('https://api.exchangerate-api.com/v4/latest/USD');
-      const rates = response.data.rates;
+      // Основной источник: ЦБ РФ (base = RUB)
+      const cbr = await axios.get('https://www.cbr-xml-daily.ru/latest.js');
+      const rubPerUsd = cbr.data && cbr.data.rates?.USD ? 1 / Number(cbr.data.rates.USD) : null;
+      const rubPerEur = cbr.data && cbr.data.rates?.EUR ? 1 / Number(cbr.data.rates.EUR) : null;
+
+      if (rubPerUsd) {
+        const eurPerUsd = rubPerEur ? rubPerUsd / rubPerEur : 1;
+        setExchangeRates({
+          USD: 1,
+          EUR: eurPerUsd,  // сколько EUR за 1 USD
+          RUB: rubPerUsd   // сколько RUB за 1 USD
+        });
+        return;
+      }
+    } catch (error) {
+      console.warn('ЦБ недоступен, пробуем резервный источник:', error?.message);
+    }
+
+    try {
+      // Резервный источник: open.er-api
+      const response = await axios.get('https://open.er-api.com/v6/latest/USD');
+      const rates = response.data?.rates || {};
       setExchangeRates({
         USD: 1,
         EUR: rates.EUR || 1,
@@ -125,7 +145,8 @@ function BillingManager() {
       });
     } catch (error) {
       console.error('Ошибка при загрузке курсов валют:', error);
-      setExchangeRates({ USD: 1, EUR: 0.85, RUB: 95 });
+      // Фолбек на разумные значения
+      setExchangeRates({ USD: 1, EUR: 1.05, RUB: 95 });
     } finally {
       setRatesLoading(false);
     }
@@ -233,11 +254,12 @@ function BillingManager() {
   }
 
   function formatCurrency(amount, currency = 'USD') {
-    if (!amount) return '—';
+    if (amount === undefined || amount === null || amount === '') return '—';
     return new Intl.NumberFormat('ru-RU', {
       style: 'currency',
       currency: currency,
-      maximumFractionDigits: 0
+      minimumFractionDigits: 2,
+      maximumFractionDigits: 2
     }).format(amount);
   }
 
@@ -246,7 +268,8 @@ function BillingManager() {
     return new Intl.NumberFormat('ru-RU', {
       style: 'currency',
       currency: 'RUB',
-      maximumFractionDigits: 0
+      minimumFractionDigits: 2,
+      maximumFractionDigits: 2
     }).format(rubAmount);
   }