Romania - Invoice Edit Currency Rate

This module is meant for companies whose country is Romania. It changes how the currency rate field behaves on customer invoices and how invoice line prices are recalculated when that rate changes.

• On the invoice form, the currency rate field becomes editable while the invoice is still in draft (for Romanian companies); for other countries it stays read-only once the invoice is no longer draft.
• When you change the currency, the invoice date or the currency rate, the unit price of each invoice line is recomputed automatically. The calculation keeps the original price in the company currency and converts it using the new rate, so the debit and credit amounts stay consistent.
• If the invoice lines come from a sales order, the module uses the sales order line price as the base. If you switch back to the sales order currency, the original sales order price is restored.
• Down payment lines are handled specially: if a posted invoice already exists for that down payment, its price is reused (converted if needed); otherwise the sales order price is used.
• The module also adjusts how the price of a down payment line is computed on sales orders for Romanian companies, converting amounts from previous invoices back into the sales order currency.

It touches the invoice (account.move) and sales order line (sale.order.line) models and adds no new menus or reports.