Confirmed orders generate confirmation record or flag

If the only record of order confirmation is the status field flipping to 'confirmed', there is no queryable timestamp for 'orders confirmed in the last 7 days', no display value for 'Confirmed on March 12' in the customer order detail view, and no audit anchor distinct from subsequent status changes. CWE-841 covers workflows where the state machine advances correctly but the associated data capture is incomplete. A confirmedAt timestamp is a lightweight addition with disproportionate operational value — it powers fulfillment metrics, SLA tracking, and customer-facing order timelines.

Add a nullable confirmedAt column to the orders table in prisma/schema.prisma and populate it during the confirmation transition in lib/orders/state-machine.ts.

// prisma/schema.prisma addition:
// confirmedAt DateTime?

// In transitionOrder (lib/orders/state-machine.ts):
const extraFields: Partial<Order> = {}
if (newStatus === 'confirmed') extraFields.confirmedAt = new Date()

await db.orders.update({
  where: { id: orderId },
  data: { status: newStatus, ...extraFields },
})