[IMP] custom_sale_purchase_display: enhance product listing

[ksoz-odoo]

Improve product selection on Sale Orders, Purchase Orders

Before:

• Products in Sale Orders were displayed in default order, unrelated to customer history.
• No indication of the last invoice date on product cards.
• Forecasted and on-hand quantities were not visible at a glance.
• No visual indicator for differences in stock levels.
• Kanban product catalog in Purchase Orders didn't showed color tags

After:

• In Sale Orders, products already sold to the selected customer are prioritized and sorted from most recent to oldest invoice.
• Remaining products appear afterward in standard order.
• Product cards in catalog view now display the last invoice date
• Forecasted quantity and on-hand quantity are shown directly on product cards.
• Stock differences are highlighted: red for negative (-), green for positive (+).

[robodoo]