feat(web): currency becomes a closed select (ALL / EUR / USD)

Currency was free text in the tariff editor (composer page + lab draft
modal — shared form) and the subscription plan editor; a typo could
publish an unknown code onto immutable versions. Both now offer a closed
select from lib/currencies.ts. An out-of-set code already stored on an
old record is appended as an extra option so it displays + round-trips
unchanged. Blank tariff form defaults to ALL (was EUR) — the site's
actual currency.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/web/src/lib/currencies.ts

@@ -0,0 +1,11 @@
+// The currencies the booth can price in (ISO 4217). Money is always stored as
+// integer minor units + one of these codes; the UI offers a closed select rather
+// than free text so a typo can never publish an unknown currency.
+export const CURRENCIES = ["ALL", "EUR", "USD"] as const;
+
+/** The select options: the known set, plus the current value when it's some
+ *  historical code outside it (so an old record still displays + round-trips). */
+export function currencyOptions(current: string): string[] {
+  const cur = current.trim().toUpperCase();
+  return cur && !CURRENCIES.includes(cur as (typeof CURRENCIES)[number]) ? [...CURRENCIES, cur] : [...CURRENCIES];
+}