feat(withdraw): 添加兑换汇率计算功能

- 新增 selectedExchangeRate 变量用于获取钻石兑换汇率
- 更新预览界面显示正确的汇率值
- 将汇率值传递给依赖数组以确保正确更新

src/hooks/use-withdraw-vm.ts

@@ -108,6 +108,9 @@ export function useWithdrawVm() {
     currencyCode,
   )
   const selectedRate = selectedCurrency.withdrawCoinsPerFiatValue || 1
+  const selectedExchangeRate =
+    config.rates.find((rate) => rate.currency === selectedCurrency.code)
+      ?.diamondsPerFiatUnitValue || selectedRate
   const sortedPayChannels = useMemo(
     () =>
       [
@@ -246,7 +249,7 @@ export function useWithdrawVm() {
       exchangeRateLabel: t('gameDesktop.withdraw.preview.exchangeRate', {
         currency: selectedCurrency.code,
       }),
-      exchangeRateValue: `1:${formatNumber(locale, selectedRate)}`,
+      exchangeRateValue: `1:${formatNumber(locale, selectedExchangeRate)}`,
       convertibleLabel: t('gameDesktop.withdraw.preview.convertible', {
         currency: selectedCurrency.code,
       }),
@@ -260,6 +263,7 @@ export function useWithdrawVm() {
       locale,
       selectedCurrency.code,
       selectedCurrency.label,
+      selectedExchangeRate,
       selectedRate,
       t,
     ],