Add currency settings, Settings service, and dialog to select fiat currency. Add support for non Official currencies like DOGE when using rates.

src/tui/components/VariableInputField.tsx

@@ -68,7 +68,7 @@ export function VariableInputField({
   focusColor,
 }: VariableInputFieldProps): React.ReactElement {
   const { currencyCode, formattedFiatPerBchRate, formatSatoshisToFiat } =
-    useSatoshisConversion("USD");
+    useSatoshisConversion();
   const satoshisValue = useMemo(
     () => parseSatoshis(variable.value),
     [variable.value],