## Problem

When generating an export CFE (e-Factura Exportación) in the Uruguayan EDI module, invoices that include a discount line equal to the subtotal — resulting in a **total of 0.00** — were not handled correctly by the XML/CFE generation
logic.

This use case is valid and required by exporters who need to reflect the declared value of goods/services while invoicing at zero (e.g. to comply with customs or incoterm requirements such as FCA). In Uruware's validation portal, the "Descuentos y Recargos" (discounts & surcharges) section of the subtotal block must be correctly populated for the CFE to be accepted.

**Example:** An invoice with a line of 648.00 UYU and a global discount of −648.00 UYU → Total: 0.00. The export value is still declared, taxes are zero, but the CFE must reflect the discount amount explicitly.

<img width="592" height="679" alt="example_expo_invoice_discount" src="https://github.com/user-attachments/assets/aa83c158-e342-4da5-a251-fc209bbed5c4" />

## Root Cause

The CFE template (`cfe_template.xml`) and the move computation logic (`account_move.py`) did not account for the case where export invoices carry line-level or global discounts that zero out the total. The discount amount was
either omitted from the XML nodes or computed incorrectly, causing Uruware validation to fail or the discount block to not render.

## Fix

- **`l10n_uy_edi/models/account_move.py`** — Updated the export invoice computation to correctly include discount amounts in the CFE data dict, ensuring the `ValorDR` is filled with the value of the discount per line.
- **`l10n_uy_edi/views/cfe_template.xml`** — Adjusted the template condition so `MntExpoyAsim` node accepts 0 as value.

## Steps to Reproduce (before fix)

1. Create an export invoice (e-Factura Exportación) for a foreign partner.
2. Add a product line with a unit price, e.g. 216.00 × 3 = 648.00 UYU.
3. Add a global discount of 648.00 (same amount) so the total is 0.00.
4. Confirm and send to Uruware — the CFE is rejected / discount block is missing.

## Verification

After the fix, the same invoice generates a valid CFE accepted by Uruware with the discount correctly reflected in the `DscRcgGlobal` node and the discount line visible on the printed document.

Forward-Port-Of: odoo/enterprise#120130