ci(qualification): add Ubuntu 24.04 k3s scenario

Description

Add an Ubuntu 24.04 k3s scenario for Kubernetes release qualification. The scenario provisions a disposable Ubuntu guest and a pinned k3s version, then exposes the cluster inputs needed by independently selected OpenShell installation profiles and testsuites.

The scenario owns guest and cluster setup only. It must not embed OpenShell installation or conformance behavior.

Context

• Parent release pipeline: #2860
• Native-install proof-of-concept pipeline: #2976
• Shared driver conformance suite: #2183
• Reusable QEMU guest infrastructure: #2471
• Installation profile model: #3419

This follows the initial Docker and Podman proof of concept and extends the same qualification composition model to a local Kubernetes environment.

Definition of Done

• The scenario provisions Ubuntu 24.04 with a pinned, supported k3s/Kubernetes version.
• The cluster is ready before qualification begins, and its effective Kubernetes version and node state are reported.
• The scenario exposes kubeconfig and cluster inputs through the shared qualification interface without embedding OpenShell installation behavior.
• The scenario can compose with the applicable OpenShell installation profile and shared conformance testsuite.
• The scenario can be invoked locally through tmachine and from GitHub Actions.
• Failure artifacts include relevant guest, systemd, k3s, Kubernetes, gateway, and sandbox diagnostics without secrets.
• Cleanup removes the disposable guest and cluster state after successful, failed, and interrupted runs.

Start by reading the shared qualification interface and installation profile model, then inspect the existing tmachine and GitHub Actions entry points for Docker and Podman scenarios. The work is complete when an Ubuntu 24.04 guest with pinned k3s provisions and cleans up reliably, exposes cluster inputs, composes with the profile and testsuite, and emits safe diagnostics.