Stock landed costs purchase auto

When a purchase order is confirmed and its receipt (transfer) is generated, this module automatically creates a landed cost document and links it to that purchase order. The same happens when a receipt is created or updated from a purchase order line, and when a backorder is created from a receipt that already has landed costs.

On the purchase order form, a smart button labelled "Landed Costs" appears in the button box (visible only to Inventory managers and only when at least one landed cost exists). Clicking it opens the list of landed costs filtered to that purchase order.

On the landed cost screen and its search filters, a new "Purchase" field is added, so users can see or search which purchase order a landed cost belongs to.

A safety check prevents creation if no default journal is configured for landed costs; in that case an error message tells the user to set it in Inventory settings.

The module touches purchase.order, purchase.order.line, stock.landed.cost and stock.picking. It does not change how landed costs are valued or posted; it only automates their creation and linking to purchases.