feat(ui-common): shared currency formatting + DJF in CurrencySelector

New lib/currency.ts is the single source of truth for currency
display across both freight web apps: symbol, name and decimals per
code (DJF is zero-decimal by convention, unlike ETB/USD). Portal's own
currency lib and backoffice's ad-hoc formatters are rewired onto this
in the next two commits instead of each guessing decimals.

CurrencySelector gets an allowDjf prop mirroring the existing allowUsd
gate, so import-shipment currency pickers can offer DJF the same way
they offer USD.

Claude-Session: https://claude.ai/code/session_01CZy77vCWhka3pnmVF9NDkL

packages/ui-common/src/components/CurrencySelector/CurrencySelector.tsx

@@ -1,10 +1,12 @@
 import { Box, Text } from "@mantine/core";
 import { Check } from "lucide-react";
 
+import type { SupportedCurrency } from "../../lib/currency";
+
 export interface CurrencySelectorProps {
   /** Selected currency code, or "" when none picked yet. */
   value: string;
-  onChange: (currency: "USD" | "ETB") => void;
+  onChange: (currency: SupportedCurrency) => void;
   disabled?: boolean;
   /** Validation error shown under the cards. */
   error?: string;
@@ -14,6 +16,12 @@ export interface CurrencySelectorProps {
    * USD is settled by bank transfer, never through the online gateway.
    */
   allowUsd?: boolean;
+  /**
+   * Offer DJF alongside ETB (and USD, if also allowed). Same import-only
+   * gating as `allowUsd` — DJF is settled both online (WAAFI / CAC Bank) and
+   * by bank transfer.
+   */
+  allowDjf?: boolean;
 }
 
 const ETB_OPTION = {
@@ -30,6 +38,13 @@ const USD_OPTION = {
   hint: "Paid by bank transfer — send the slip to Finance",
 } as const;
 
+const DJF_OPTION = {
+  code: "DJF",
+  symbol: "Fdj",
+  name: "Djibouti Franc",
+  hint: "Pay online, or by bank transfer — send the slip to Finance",
+} as const;
+
 /**
  * Card-style USD/ETB billing-currency picker. Renders unselected when `value`
  * is "" so a required choice never looks pre-made.
@@ -40,8 +55,13 @@ export function CurrencySelector({
   disabled = false,
   error,
   allowUsd = false,
+  allowDjf = false,
 }: CurrencySelectorProps) {
-  const options = allowUsd ? [ETB_OPTION, USD_OPTION] : [ETB_OPTION];
+  const options = [
+    ETB_OPTION,
+    ...(allowUsd ? [USD_OPTION] : []),
+    ...(allowDjf ? [DJF_OPTION] : []),
+  ];
   return (
     <Box>
       <Box