fix(tui): should primarily (or only) show Cayo, Snow, and SnowField OS images in menu

[bsherman]

Currently it has:

  Step 2 of 9: OS Image

┃ OS Image
┃ Select the bootc image to install, or choose Custom to enter a URL.
┃ > Bluefin (Fedora-based, GNOME)
┃   Aurora (Fedora-based, KDE)
┃   CentOS Stream 10
┃   Debian
┃   Arch Linux
┃   Custom URL...

We should instead offer:

• Cayo
• Snow
• Snowfield
• Custom URL...