Feature: Add order tracking and shipping status updates

- Add carrier, trackingNumber, and estimatedDeliveryDate fields to Order model
- Update order statuses: PENDING, PAID, PRINTING, PRINTED, SHIPPED, DELIVERED, FAILED
- Add admin UI on order detail page to update tracking information
- Display tracking info on customer account page in order history
- Server action to update order tracking and status

Customers can now see their shipping status and tracking details from
their account page. Admins can update order status and tracking info
from the order detail page.

prisma/schema.prisma

@@ -218,9 +218,15 @@ model Order {
   stripeSessionId String?     @unique
   email           String?
   shippingAddress String? // JSON — collected by Stripe Checkout, saved once payment completes
-  status          String      @default("PENDING") // PENDING | PAID | FAILED
+  status          String      @default("PENDING") // PENDING | PAID | PRINTING | PRINTED | SHIPPED | DELIVERED | FAILED
   archived        Boolean     @default(false)
   total           Int // cents
+
+  // Shipping & tracking info
+  carrier         String? // e.g. "Royal Mail", "DPD", "Courier"
+  trackingNumber  String? // tracking number from carrier
+  estimatedDeliveryDate DateTime? // estimated delivery date
+
   createdAt       DateTime    @default(now())
   updatedAt       DateTime    @updatedAt