Sale Coupon Promotion Product Domain Discount

This module extends the coupon promotion feature in Sales so that a discount program can be restricted to a set of products defined by a product domain.

When a promotion is configured to apply on specific products and to use a product domain, the discount is calculated only on the order lines whose products match that domain. Products outside the domain are not discounted.

If the promotion also uses the strict per-product limit option, the module checks each matching product individually: the product must reach the minimum quantity and the minimum amount (tax included or excluded, depending on the promotion setting) before its lines are included in the discount. Only lines that pass this check are discounted.

This affects the sale.order model when reward discount values are computed, and the coupon.program model when deciding which reward programs are still available for an order. There are no new menus or screens; the behaviour is added to the existing promotion setup and sale order discount calculation.