feat(loyalty): show what an order earned on the order and receipt

Adds points_earned and coins_earned to the order response
(docs/prd-point-coin.md F3, PC-205). The POS prints the receipt from this
response, so the receipt gets them too.

The values are the sums of the order's EARN rows, read in one query for a
list of orders. They are filled for create, add items, update, detail and
list, and are 0 for an order that earned nothing. UpdateOrder earns before
building its response, so a payment completed there already shows the
earning. A failure to read them is logged and leaves them at 0 rather than
failing the order read. The self-order session listing reads orders
directly from the repository and still shows 0.

The two order hooks are merged into one OrderLoyalty interface (paid,
refunded, earned by orders) with a single SetLoyalty.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/models/order.go

@@ -182,6 +182,9 @@ type OrderResponse struct {
 	TotalPaid       float64
 	PaymentCount    int
 	SplitType       *string
+	// What the order earned (docs/prd-point-coin.md F3), from its EARN rows.
+	PointsEarned int64
+	CoinsEarned  int64
 }
 
 type OrderItemResponse struct {