Account Invoice Discount Display Amount

This module adds two new amounts to customer invoices: the total discount applied and the total without discount. These amounts are calculated automatically from the invoice lines.

On each invoice line, the module computes the discount amount and the line total before discount. For lines with a discount, the total before discount is recalculated including taxes, and the discount is the difference between that amount and the line total. Lines that are not products (for example section or note lines) show zero.

On the invoice itself, the module adds up the line values to show a total discount and a total without discount. These totals are only calculated for invoices; other types of accounting entries show zero.

In the Odoo backend, the two new amounts appear on the invoice form, right after the tax totals block. On the invoice PDF report, a new line labelled "Discount" is added after the tax totals, showing the total discount amount.

The module works on account.move and account.move.line and does not change any other accounting behaviour.