Stock Valuation Layer no developer mode

This module changes who can see the Valuation button on stock transfer (picking) screens. Normally that button is only shown when developer mode is turned on, which makes it hard for regular business users to reach stock valuation information.

With this module installed, the button is instead shown to users who belong to the Billing accounting group. That means accountants and billing users can open the stock valuation layers directly from a transfer, without needing technical/debug access.

• It only affects the stock transfer screen (stock.picking).
• It does not create new menus or new screens; it simply adjusts the visibility rule of the existing Valuation button.
• No new calculations, checks, emails or scheduled jobs are added.
• The change is limited to the button that opens stock valuation layers; other stock accounting behaviour stays as provided by the standard Stock Accounting app.

Because the module only overrides a view attribute, its effect is purely about access/visibility. If a user is not in the Billing group, the button remains hidden for them, just as before.