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.
