Price recalculation in purchases orders

This module adds a single button to the purchase order form, placed next to the existing unlock button. The button is labelled 'Update lines info' and shows a refresh icon.

• It is only visible while the purchase order is in Draft or Sent status, so it cannot be used on confirmed or locked orders.
• When clicked, a confirmation message appears: 'This will update all the line prices based on the vendor currently set. Do you want to continue?' This gives the user the choice to recalculate or cancel.
• If confirmed, every order line is recalculated using the current vendor's product information, updating the unit price, the planned date and the line description.

This is useful after changing the vendor on a purchase order or after duplicating one, because Odoo does not automatically refresh line prices in those situations. The module only touches the purchase.order model and its form view; it does not add menus, reports, scheduled jobs or automatic rules.