Product Cost Security

This module protects the product cost price (standard_price) on both product.template and product.product with two new access groups under a "Product costs" privilege: "Read" lets a user see the cost, and "Edit" lets a user change it. The "Edit" group automatically includes the "Read" group, so anyone who can edit costs can also see them.

• Users who are not in the "Read" group do not see the cost price field on the product form; the field is hidden by the security group applied to the product form view.
• Users who can see the cost but are not in the "Edit" group get the cost field shown as read-only, and any attempt to write to it is blocked with an access error message telling them to contact their system administrator.
• A computed flag user_can_update_cost tells the interface whether the current user is allowed to change costs, and the field metadata is adjusted so the cost appears read-only when editing is not allowed.
• The protection is applied through a reusable mixin (product.cost.security.mixin) that other modules can inherit to secure their own cost-related fields.

The module only touches the product area: the product form view and the cost price fields on product templates and product variants. It does not add menus, reports, or scheduled actions.