feat: voucher crud and list

lib/vouchers.ts

@@ -0,0 +1,12 @@
+export type VoucherInput = { name: string; anbieter: string; wertCents: number; restCents: number; ablaufdatum: string | null; codeText?: string | null; kategorie?: string | null; notiz?: string | null; };
+export function validateVoucher(v: VoucherInput): string[] {
+  const errs: string[] = [];
+  if (!v.name?.trim()) errs.push("name");
+  if (!v.anbieter?.trim()) errs.push("anbieter");
+  if (!Number.isInteger(v.wertCents) || v.wertCents <= 0) errs.push("wertCents");
+  if (!Number.isInteger(v.restCents) || v.restCents < 0 || v.restCents > v.wertCents) errs.push("restCents");
+  return errs;
+}
+export function formatEuro(cents: number): string {
+  return (cents / 100).toLocaleString("de-DE", { style: "currency", currency: "EUR" });
+}