linuxlive 0.3.0: Fedora installs

Fedora-based ISOs now install too, with the same Install desktop icon, Install boot-menu entry and installer as Ubuntu's. The installer runs bootc install to-disk from the system image the build published, so:

• Callers that build Fedora-based specs set publish-image: true and grant packages: write. The build pushes the image to ghcr.io/<owner>/<repo>/<name>, tagged run-<id>, and :latest once the build is verified.
• Installing needs the internet. Installed systems follow :latest, so bootc upgrade brings each newer verified build.
• A first-boot service creates your user before the login screen starts. The installer icon, Plasma Welcome and upstream's first-login setup are left out of the installed system. Autologin works on GNOME, KDE (Plasma Login Manager) and Cinnamon.

The live KDE session no longer opens Plasma Welcome. CI installs all four examples unattended in QEMU and boots each installed disk under UEFI with Secure Boot and under BIOS. For Fedora, verify-results checks that the system runs the published image from xfs. Proven by run 38521159901.

Not yet: dual boot, encryption, and offline installs of Fedora-based ISOs. To upgrade, change @v0.2.0 to @v0.3.0 in your workflow and add the two lines above.