Add-on: AL13 3PC Cap Upgrade (per wheel)

Hidden add-on line item. Added automatically to the cart once per wheel when a customer selects the 3PC Cap Upgrade option (includes carbon logos and titanium bolts) on an AL13 forged wheel. Hidden from the storefront on purpose: it has no images, no collection and is not meant to be found or bought on its own. Its price here is the single source of truth — editing it in admin updates both the price shown on the wheel page and the amount actually charged at checkout, with no code change. Do not rename the handle — the wheel template looks this product up by handle, and renaming it silently drops the upcharge from the configurator.