Purchase Stock Picking Invoice Link

This module connects the three documents of a purchase cycle: the purchase order, the stock movements (receipts and returns) and the vendor bill. It works together with the stock picking/invoice link and purchase-stock features, and installs automatically when those are present.

What it changes for users: - When a vendor bill is created from a purchase order, the invoice lines are automatically linked to the relevant completed stock movements, so the invoice keeps a trace of the receipts it covers. - On a purchase order line, the system looks at the product's invoicing policy: quantities are taken from ordered quantities when the product is invoiced on order, or from received quantities when it is invoiced on receipt. - Only finished (done) movements are considered; scrapped moves are ignored. Returns to the supplier are handled as refunds and linked to credit notes. - If more has already been invoiced than ordered/received, only return movements are linked, avoiding wrong links on over-invoiced lines. - When a receipt is validated after the bill was already created (for products invoiced on order), the module searches existing vendor bills or credit notes for that purchase line and links the stock movement to them automatically.

It touches purchase.order.line, stock.move and account.move.line, and relies on the standard purchase, stock and accounting screens rather than adding new menus.