💱 feat(settings): introduce site-wide quota display type (USD/CNY/TOKENS/CUSTOM)

Replace the legacy boolean “DisplayInCurrencyEnabled” with an injected, type-safe
configuration `general_setting.quota_display_type`, and wire it through the
backend and frontend.

Backend
- Add `QuotaDisplayType` to `operation_setting.GeneralSetting` with injected
  registration via `config.GlobalConfig.Register("general_setting", ...)`.
  Helpers: `IsCurrencyDisplay()`, `IsCNYDisplay()`, `GetQuotaDisplayType()`.
- Expose `quota_display_type` in `/api/status` and keep legacy
  `display_in_currency` for backward compatibility.
- Logger: update `LogQuota` and `FormatQuota` to support USD/CNY/TOKENS. When
  CNY is selected, convert using `operation_setting.USDExchangeRate`.
- Controllers:
  - `billing`: compute subscription/usage amounts based on the selected type
    (USD: divide by `QuotaPerUnit`; CNY: USD→CNY; TOKENS: keep raw tokens).
  - `topup` / `topup_stripe`: treat inputs as “amount” for USD/CNY and as
    token-count for TOKENS; adjust min topup and pay money accordingly.
  - `misc`: include `quota_display_type` in status payload.
- Compatibility: in `model/option.UpdateOption`, map updates to
  `DisplayInCurrencyEnabled` → `general_setting.quota_display_type`
  (true→USD, false→TOKENS). Keep exporting the legacy key in `OptionMap`.

Frontend
- Settings: replace the “display in currency” switch with a Select
  (`general_setting.quota_display_type`) offering USD / CNY / Tokens.
  Provide fallback mapping from legacy `DisplayInCurrencyEnabled`.
- Persist `quota_display_type` to localStorage (keep `display_in_currency`
  for legacy components).
- Rendering helpers: base all quota/price rendering on `quota_display_type`;
  use `usd_exchange_rate` for CNY symbol/values.
- Pricing page: default view currency follows site display type (USD/CNY),
  while TOKENS mode still allows per-view currency toggling when needed.

Notes
- No database migrations required.
- Legacy clients remain functional via compatibility fields.

web/src/hooks/model-pricing/useModelPricingData.jsx

@@ -64,6 +64,29 @@ export const useModelPricingData = () => {
     () => statusState?.status?.usd_exchange_rate ?? priceRate,
     [statusState, priceRate],
   );
+  const customExchangeRate = useMemo(
+    () => statusState?.status?.custom_currency_exchange_rate ?? 1,
+    [statusState],
+  );
+  const customCurrencySymbol = useMemo(
+    () => statusState?.status?.custom_currency_symbol ?? '¤',
+    [statusState],
+  );
+
+  // 默认货币与站点展示类型同步（USD/CNY），TOKENS 时仍允许切换视图内货币
+  const siteDisplayType = useMemo(
+    () => statusState?.status?.quota_display_type || 'USD',
+    [statusState],
+  );
+  useEffect(() => {
+    if (
+      siteDisplayType === 'USD' ||
+      siteDisplayType === 'CNY' ||
+      siteDisplayType === 'CUSTOM'
+    ) {
+      setCurrency(siteDisplayType);
+    }
+  }, [siteDisplayType]);
 
   const filteredModels = useMemo(() => {
     let result = models;
@@ -156,6 +179,8 @@ export const useModelPricingData = () => {
 
     if (currency === 'CNY') {
       return `¥${(priceInUSD * usdExchangeRate).toFixed(3)}`;
+    } else if (currency === 'CUSTOM') {
+      return `${customCurrencySymbol}${(priceInUSD * customExchangeRate).toFixed(3)}`;
     }
     return `$${priceInUSD.toFixed(3)}`;
   };