POS Barcode Block

This module changes how the Point of Sale behaves when a barcode is scanned that Odoo cannot match to any product.

• Normally the POS only shows a small notification for an unknown code. With this module, a blocking alert dialog titled "Unknown Barcode" appears instead, with the message "No product found associated with code: ..." showing the scanned code.
• While this alert is open, the barcode reader is blocked: any further scans are ignored, so the cashier cannot keep scanning products until the dialog is closed.
• Closing the alert releases the block and scanning works again as usual.

The change is applied to the POS store logic (PosStore), which is the central component that manages the Point of Sale session and its barcode reader. No new menus, models, reports or scheduled actions are added; the module only alters the existing scanning behaviour inside the Point of Sale screen. It depends on the standard Point of Sale app (point_of_sale).