feat(domain): add domain types

src/domain/types.test.ts

@@ -0,0 +1,12 @@
+import { test, expect } from "bun:test";
+import { CURRENCIES, CURRENCY_DIGITS } from "./types.ts";
+
+test("supported currencies are exactly DKK, USD, EUR", () => {
+  expect(CURRENCIES).toEqual(["DKK", "USD", "EUR"]);
+});
+
+test("every supported currency has 2 decimal digits", () => {
+  for (const c of CURRENCIES) {
+    expect(CURRENCY_DIGITS[c]).toBe(2);
+  }
+});