Support native browser notifications in Web applications

Allow Objo Web applications to show native browser and operating-system notifications for significant or time-sensitive events. Applications should be able to discover whether notifications are supported, ask the user for permission through an explicit interaction, and show a notification when permission has been granted. Permission denial and unsupported browsers must be predictable and must not prevent the application from continuing normally.

This feature is distinct from in-page toast notifications: the browser or operating system owns native-notification appearance, placement, lifetime, and notification-centre integration.