Sale Exception Public Holidays

This module plugs into the sales exception framework and the public holidays data to check delivery dates on sales orders.

When a sales order has a commitment date (the promised delivery date), the module looks at the shipping address of the order and checks whether that date is a public holiday for that address's country and state. If it is, the order can be flagged with the exception "Delivery Date is a public holiday".

• The exception rule is created but is inactive by default, so nothing changes until someone enables it in the exception rules settings.
• Once enabled, the check runs automatically whenever the commitment date is set or changed on a sales order.
• The check uses the shipping partner's country and state to find matching public holiday lines; holidays defined without a specific state also count.
• The rule is attached to the sale.order model, so it appears in the standard sales exception workflow (for example, blocking confirmation or showing a warning, depending on how the exception rule is configured).

No new menus or screens are added; the feature is managed through the existing exception rules configuration and the sales order form.