Add per-quantity TPago payment links for multi-ticket checkout.

Each ticket quantity (1-5) can have its own TPago link so checkout, emails, and admin config use the correct fixed-amount URL.

frontend/src/lib/utils.ts

@@ -165,3 +165,31 @@ export function formatPrice(price: number, currency: string = 'PYG'): string {
 export function formatCurrency(amount: number, currency: string = 'PYG'): string {
   return formatPrice(amount, currency);
 }
+
+// ---------------------------------------------------------------------------
+// Payment helpers
+// ---------------------------------------------------------------------------
+
+type TpagoLinkConfig = {
+  tpagoLink?: string | null;
+  tpagoLink2?: string | null;
+  tpagoLink3?: string | null;
+  tpagoLink4?: string | null;
+  tpagoLink5?: string | null;
+};
+
+/**
+ * Select the TPago payment link that matches the number of tickets being
+ * purchased (1-5). Each link has a fixed amount baked in, so the quantity
+ * determines which one to use. Falls back to the base (1-ticket) link when a
+ * specific quantity link isn't configured.
+ */
+export function getTpagoLink(
+  config: TpagoLinkConfig | null | undefined,
+  ticketCount: number
+): string | null {
+  if (!config) return null;
+  const count = Math.min(Math.max(1, Math.floor(ticketCount || 1)), 5);
+  const key = (count <= 1 ? 'tpagoLink' : `tpagoLink${count}`) as keyof TpagoLinkConfig;
+  return config[key] || config.tpagoLink || null;
+}