Sale Stock Available Info Popup

This module enriches the stock information popover that appears on sale order lines with an extra line called 'Available to promise'.

• On each sale order line, a new computed quantity is calculated: the product's immediately usable quantity, taken for the line's warehouse and scheduled date.
• The calculation respects the order of the lines: if the same product appears on several lines, the quantity already committed to earlier lines is subtracted, so each line shows what is still genuinely available for it.
• Quantities are converted between the product's unit of measure and the line's unit of measure when they differ.
• The value is only computed for lines that have a product and that display the quantity widget.

The result is displayed in the popover that opens from the quantity-at-date widget on sale order lines, both in the order lines list and in the order line form dialog. The popover shows the 'Available to promise' figure next to the line's unit of measure.

It touches the sale order line model (sale.order.line) and relies on the stock availability logic from the stock_available module. No new menus, buttons, checks or scheduled jobs are added; the module only adds information to an existing screen.