The rate matrix currency cell hardcoded USD, so a last-mile rate
priced in ETB still displayed as dollars. formatCell now takes the
row and reads its currency code, falling back to USD.
Last-mile currency select gets defaultValue ETB (new generic
FormFieldDef.defaultValue for create-time pre-selection) and lists
ETB (Birr) first; USD stays selectable. Backend already persisted
and validated the chosen currency.