feat(currency): add Belize Dollars (BZD) to currency dropdown (#1454)

Adds BZD with symbol BZ$ to the Settings cost-currency picker so
  users in Belize can track filament costs in their local currency
  without doing 2:1 USD mental conversions.

frontend/src/utils/currency.ts

@@ -19,6 +19,7 @@ const CURRENCY_SYMBOLS: Record<string, string> = {
   SGD: 'S$',
   NZD: 'NZ$',
   MXN: 'MX$',
+  BZD: 'BZ$',
   MYR: 'RM',
   CZK: 'Kč',
   THB: '฿',