💱 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.

setting/operation_setting/general_setting.go

@@ -2,17 +2,34 @@ package operation_setting
 
 import "one-api/setting/config"
 
+// 额度展示类型
+const (
+	QuotaDisplayTypeUSD    = "USD"
+	QuotaDisplayTypeCNY    = "CNY"
+	QuotaDisplayTypeTokens = "TOKENS"
+	QuotaDisplayTypeCustom = "CUSTOM"
+)
+
 type GeneralSetting struct {
 	DocsLink            string `json:"docs_link"`
 	PingIntervalEnabled bool   `json:"ping_interval_enabled"`
 	PingIntervalSeconds int    `json:"ping_interval_seconds"`
+	// 当前站点额度展示类型：USD / CNY / TOKENS
+	QuotaDisplayType string `json:"quota_display_type"`
+	// 自定义货币符号，用于 CUSTOM 展示类型
+	CustomCurrencySymbol string `json:"custom_currency_symbol"`
+	// 自定义货币与美元汇率（1 USD = X Custom）
+	CustomCurrencyExchangeRate float64 `json:"custom_currency_exchange_rate"`
 }
 
 // 默认配置
 var generalSetting = GeneralSetting{
-	DocsLink:            "https://docs.newapi.pro",
-	PingIntervalEnabled: false,
-	PingIntervalSeconds: 60,
+	DocsLink:                   "https://docs.newapi.pro",
+	PingIntervalEnabled:        false,
+	PingIntervalSeconds:        60,
+	QuotaDisplayType:           QuotaDisplayTypeUSD,
+	CustomCurrencySymbol:       "¤",
+	CustomCurrencyExchangeRate: 1.0,
 }
 
 func init() {
@@ -23,3 +40,52 @@ func init() {
 func GetGeneralSetting() *GeneralSetting {
 	return &generalSetting
 }
+
+// IsCurrencyDisplay 是否以货币形式展示（美元或人民币）
+func IsCurrencyDisplay() bool {
+	return generalSetting.QuotaDisplayType != QuotaDisplayTypeTokens
+}
+
+// IsCNYDisplay 是否以人民币展示
+func IsCNYDisplay() bool {
+	return generalSetting.QuotaDisplayType == QuotaDisplayTypeCNY
+}
+
+// GetQuotaDisplayType 返回额度展示类型
+func GetQuotaDisplayType() string {
+	return generalSetting.QuotaDisplayType
+}
+
+// GetCurrencySymbol 返回当前展示类型对应符号
+func GetCurrencySymbol() string {
+	switch generalSetting.QuotaDisplayType {
+	case QuotaDisplayTypeUSD:
+		return "$"
+	case QuotaDisplayTypeCNY:
+		return "¥"
+	case QuotaDisplayTypeCustom:
+		if generalSetting.CustomCurrencySymbol != "" {
+			return generalSetting.CustomCurrencySymbol
+		}
+		return "¤"
+	default:
+		return ""
+	}
+}
+
+// GetUsdToCurrencyRate 返回 1 USD = X <currency> 的 X（TOKENS 不适用）
+func GetUsdToCurrencyRate(usdToCny float64) float64 {
+	switch generalSetting.QuotaDisplayType {
+	case QuotaDisplayTypeUSD:
+		return 1
+	case QuotaDisplayTypeCNY:
+		return usdToCny
+	case QuotaDisplayTypeCustom:
+		if generalSetting.CustomCurrencyExchangeRate > 0 {
+			return generalSetting.CustomCurrencyExchangeRate
+		}
+		return 1
+	default:
+		return 1
+	}
+}