Event website visitors now see a dedicated offline page when their connection is lost or cached content cannot be used. This improves the experience for attendees by clearly handling connectivity issues and automatically refreshing content once the connection returns.

This page will be used in case of lost connection. The web page will be
automatically fetched when you are back online.

We also use this page when it's not possible to use the cache due to a
redirection.

X-original-commit: a7c5cadc7467bd2c2423cd3e803cad3677961521

The IoT app now uses a clearer and more consistent name for device display links, while removing an unused box field. This reduces internal clutter and helps keep future IoT setup and maintenance simpler without changing the user workflow.

Remove unused screen_url field from iot.box and rename screen_url to
display_url for consistency.

TaskID: 1973956