💱 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/components/settings/personal/cards/AccountManagement.jsx

@@ -85,7 +85,8 @@ const AccountManagement = ({
     );
   };
   const isBound = (accountId) => Boolean(accountId);
-  const [showTelegramBindModal, setShowTelegramBindModal] = React.useState(false);
+  const [showTelegramBindModal, setShowTelegramBindModal] =
+    React.useState(false);
 
   return (
     <Card className='!rounded-2xl'>
@@ -226,7 +227,8 @@ const AccountManagement = ({
                         onGitHubOAuthClicked(status.github_client_id)
                       }
                       disabled={
-                        isBound(userState.user?.github_id) || !status.github_oauth
+                        isBound(userState.user?.github_id) ||
+                        !status.github_oauth
                       }
                     >
                       {status.github_oauth ? t('绑定') : t('未启用')}
@@ -384,7 +386,8 @@ const AccountManagement = ({
                         onLinuxDOOAuthClicked(status.linuxdo_client_id)
                       }
                       disabled={
-                        isBound(userState.user?.linux_do_id) || !status.linuxdo_oauth
+                        isBound(userState.user?.linux_do_id) ||
+                        !status.linuxdo_oauth
                       }
                     >
                       {status.linuxdo_oauth ? t('绑定') : t('未启用')}