Shows the inverse of the existing "1 BTC to <currency>" rate — how
many Sats one unit of the default currency is worth — right below it.
Useful since many currencies are worth less than, or a low multiple
of, a single Sat.
CurrencyConverter.satsPerCurrencyUnit(rate) does the actual division;
ConverterUiState.oneCurrencyToSats() derives the display string from
the already-fetched rate the same way defaultCurrencyRate() does, so
no new ViewModel state was needed. Wired into both Compose and the
iOS bridge/SwiftUI.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FXcrACM5sok3M1KQJ8kByy