Point of Sale Fixed Discounts

This module extends the Point of Sale discount feature. On the POS product screen, next to the existing percentage discount button, a new button labelled "Discount (Amount)" appears (the percentage button is relabelled "Discount (%)").

When the cashier taps the new button, a popup titled "Discount Amount" opens asking for a number. After confirmation, the module removes any previous discount lines from the current order and adds a single discount line with the entered amount as a negative price, so the order total is reduced by that fixed amount.

The button is only shown when the Point of Sale configuration has the discount module enabled and a discount product configured. If that discount product cannot be found, an error popup explains that the discount product is misconfigured and must be marked as "Can be Sold" and "Available in Point of Sale".

The discount line price is set manually so it is not recalculated when the customer changes. The module works entirely inside the Point of Sale interface and does not add new database models or menus.