Order Detail Screen

Shows a single Order. For customers: items, tracking timeline, shipping address, totals, 'view receipt' CTA. For sellers: also customer block, split-payment status, Cancel button with confirmation dialog.

1. Reads orderId from the GoRouter path param.
2. Consumes orderDetailProvider(orderId).
3. Customer flow: TrackingTimeline shows fulfillmentStatus progression; Receipt button pushes ReceiptScreen.
4. Seller flow: Cancel button → confirmation dialog → cancelSellerOrderProvider(orderId).future → re-fetch detail.
5. Error / loading states are rendered via AsyncValue.when().

• Cancelled orders disable the Cancel button and surface 'Refunded €X' computed from splitOrderPayment.refundedAmount.
• Tracking timeline interprets fulfillment_status into steps: pending → fulfilled → shipped → delivered.
• Seller has no 'view receipt' (no CTA implemented yet) — that's a customer-only flow.

• lib/src/features/shared/orders/views/order_detail_screen.dart
• lib/src/features/shared/orders/views/widgets/tracking_timeline.dart

Long screen (~1k lines) with inline subwidgets — pulling them out into widgets/* would simplify cross-role testing.