chore(seed): seed an active flash sale

Add one active session for the demo shop with a discounted activity item on one
of its SKUs, idempotent by English label, so the live mall has a discoverable
flash sale to check out.

scripts/seed-demo.mjs

@@ -368,6 +368,47 @@ const POINTS_PRODUCTS = [
   console.log(`points products ready: ${POINTS_PRODUCTS.length} (${created} new)`);
 }
 
+// 7. an active flash sale for the demo shop (idempotent by English label).
+{
+  const owner = ownerTokens.get("demo-store");
+  const listed = await call("GET", "/shop/flash-sales", { token: owner });
+  if (listed.status !== 200) fail("list flash sales", listed);
+  const known = new Set(listed.data.map((s) => s.label.en));
+  if (!known.has("Weekend flash sale")) {
+    const products = await call("GET", "/shop/products?per_page=100", { token: owner });
+    if (products.status !== 200) fail("list shop products", products);
+    const sku = (products.data.items ?? [])
+      .flatMap((p) => p.skus ?? [])
+      .find((s) => s.active && s.stock > 0);
+    if (!sku) fail("find a flash-sale SKU", { status: 0, data: "no active SKU" });
+
+    const now = Date.now();
+    const session = await call("POST", "/shop/flash-sales", {
+      token: owner,
+      body: {
+        label: { en: "Weekend flash sale", zh: "周末秒杀" },
+        starts_at: new Date(now - 3600 * 1000).toISOString(),
+        ends_at: new Date(now + 7 * 24 * 3600 * 1000).toISOString(),
+        enabled: true,
+      },
+    });
+    if (session.status !== 201) fail("seed flash session", session);
+
+    const item = await call("POST", `/shop/flash-sales/${session.data.id}/items`, {
+      token: owner,
+      body: {
+        sku_id: sku.id,
+        sale_price_minor: Math.max(1, Math.round(sku.price_minor * 0.6)),
+        currency: sku.currency,
+        reserved_stock: 20,
+        per_customer_limit: 2,
+      },
+    });
+    if (item.status !== 201) fail("seed flash item", item);
+  }
+  console.log("flash sale ready");
+}
+
 console.log("\nDemo data seeded.");
 console.log("  platform admin : admin@vmall.local / admin1234   (apps/admin :3002)");
 console.log("  shop owner     : shop@vmall.local / shop12345    (apps/shop-admin :3001)");