[BUG]: offline mode impossible

### What happened? Provisioning an image _may_ depends upon remote resources (list of versions, firmwares, ...) : this is understandable. But making it **mandatory** is definitely unexpected since network is an **optional** aspect of provisioning (we may want to do that in an isolated environment, controlling the few strictly input, eg URLs / list of distributions / and related JSON data ...) So why in the first is this app' unusable without an internet network? Sounds like one of these newer Windows installers and their mandatory phone-home built-in "features". ### Version 2.0.9 (Default) ### What host operating system were you using? Debian and derivatives (eg Ubuntu) ### Host OS Version Ubuntu 24 ### Selected OS 2026-04-21-raspios-trixie-arm64-lite ### Which Raspberry Pi Device are you using? Raspberry Pi Zero 2 W ### What kind of storage device are you using? microSD Card in an internal reader ### OS Customisation - [ ] Yes, I was using OS Customisation when the bug occurred. ### Relevant log output Network jail under which `rpi-imager` must still be functioning: <!-- Failed to upload "rpi-imager.profile.txt" -->