Add Relay returns and QR checkout demo

dist/payments.mjs

@@ -0,0 +1,16 @@
+import qrcode from "./vendor/qrcode.mjs";
+
+export function parsePaymentLink(value) {
+  let url;
+  try { url = new URL(value.trim()); } catch { return null; }
+  if (url.origin !== "https://buy.stripe.com" || url.username || url.password ||
+      !/^\/(?:test_)?[A-Za-z0-9]{6,150}$/.test(url.pathname) || url.search || url.hash) return null;
+  return {href:url.href,test:url.pathname.startsWith("/test_")};
+}
+
+export function qrImage(href) {
+  const qr = qrcode(0,"M");
+  qr.addData(href);
+  qr.make();
+  return qr.createDataURL(6,24);
+}