ci(qualification): add Linux proof-of-concept scenarios #2973

Description

Add the Linux scenarios used by the initial release qualification proof of concept:

• Ubuntu 24.04 with rootful Docker;
• Fedora with rootful Podman and SELinux enforcing;
• Fedora with rootless Podman and SELinux enforcing.

Each scenario owns machine and container-runtime setup. OpenShell installation and post-install behavior remain independently selected through installation profiles and testsuites.

Context

• Parent release pipeline: feat: 0.1.0 release pipeline #2860
• Proof-of-concept pipeline: ci(qualification): run native Linux proof-of-concept pipeline #2976
• Reusable release artifacts: chore(ci): clean up release pipeline #1683
• Reusable QEMU guest infrastructure: test(e2e): add reusable QEMU infrastructure for E2E tests #2471
• VM-backed E2E runner: test(e2e): add VM-backed E2E suite runner #2473
• Installation profile model: refactor(tmachine): separate installation profiles #3419

These scenarios establish the first portable Linux qualification matrix without coupling host provisioning to native, DEB, or RPM installation behavior.

Definition of Done

• The Ubuntu scenario uses Ubuntu 24.04 with rootful Docker.
• Fedora scenarios cover both rootful and rootless Podman.
• Both Fedora scenarios verify that SELinux is enforcing before qualification begins.
• Scenario setup contains no OpenShell installation or testsuite behavior.
• Each scenario can be invoked locally through tmachine and from GitHub Actions.
• Failure artifacts include relevant guest, systemd, container-runtime, SELinux, gateway, and sandbox diagnostics without secrets.
• Cleanup is reliable after successful, failed, and interrupted runs.