💱 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/pages/Setting/Ratio/ModelRatioSettings.jsx

@@ -226,8 +226,12 @@ export default function ModelRatioSettings(props) {
           <Col xs={24} sm={16}>
             <Form.TextArea
               label={t('图片输入倍率（仅部分模型支持该计费）')}
-              extraText={t('图片输入相关的倍率设置，键为模型名称，值为倍率，仅部分模型支持该计费')}
-              placeholder={t('为一个 JSON 文本，键为模型名称，值为倍率，例如：{"gpt-image-1": 2}')}
+              extraText={t(
+                '图片输入相关的倍率设置，键为模型名称，值为倍率，仅部分模型支持该计费',
+              )}
+              placeholder={t(
+                '为一个 JSON 文本，键为模型名称，值为倍率，例如：{"gpt-image-1": 2}',
+              )}
               field={'ImageRatio'}
               autosize={{ minRows: 6, maxRows: 12 }}
               trigger='blur'
@@ -238,9 +242,7 @@ export default function ModelRatioSettings(props) {
                   message: '不是合法的 JSON 字符串',
                 },
               ]}
-              onChange={(value) =>
-                setInputs({ ...inputs, ImageRatio: value })
-              }
+              onChange={(value) => setInputs({ ...inputs, ImageRatio: value })}
             />
           </Col>
         </Row>
@@ -249,7 +251,9 @@ export default function ModelRatioSettings(props) {
             <Form.TextArea
               label={t('音频倍率（仅部分模型支持该计费）')}
               extraText={t('音频输入相关的倍率设置，键为模型名称，值为倍率')}
-              placeholder={t('为一个 JSON 文本，键为模型名称，值为倍率，例如：{"gpt-4o-audio-preview": 16}')}
+              placeholder={t(
+                '为一个 JSON 文本，键为模型名称，值为倍率，例如：{"gpt-4o-audio-preview": 16}',
+              )}
               field={'AudioRatio'}
               autosize={{ minRows: 6, maxRows: 12 }}
               trigger='blur'
@@ -260,9 +264,7 @@ export default function ModelRatioSettings(props) {
                   message: '不是合法的 JSON 字符串',
                 },
               ]}
-              onChange={(value) =>
-                setInputs({ ...inputs, AudioRatio: value })
-              }
+              onChange={(value) => setInputs({ ...inputs, AudioRatio: value })}
             />
           </Col>
         </Row>
@@ -270,8 +272,12 @@ export default function ModelRatioSettings(props) {
           <Col xs={24} sm={16}>
             <Form.TextArea
               label={t('音频补全倍率（仅部分模型支持该计费）')}
-              extraText={t('音频输出补全相关的倍率设置，键为模型名称，值为倍率')}
-              placeholder={t('为一个 JSON 文本，键为模型名称，值为倍率，例如：{"gpt-4o-realtime": 2}')}
+              extraText={t(
+                '音频输出补全相关的倍率设置，键为模型名称，值为倍率',
+              )}
+              placeholder={t(
+                '为一个 JSON 文本，键为模型名称，值为倍率，例如：{"gpt-4o-realtime": 2}',
+              )}
               field={'AudioCompletionRatio'}
               autosize={{ minRows: 6, maxRows: 12 }}
               trigger='blur'