Apply service plan discount to a specific line item

Let a service plan discount target a specific line item (e.g. the exterior window cleaning) instead of only coming off the job total. Today the plan discount always applies to the whole job, so add-ons like screen cleaning look discounted too. Customers want the discount to visibly sit on the plan's core service.

Customer quote: "I'm just trying to take $50 off of the exterior window screen… I want the $50 to reflect on the exterior cleaning."

Customer: Stefano Fernandez — Heights Soft Wash / Heights Window Cleaning (Tampa, FL)
Call: https://fathom.video/calls/870033397