test(tmachine): pin k3s to Kubernetes 1.29

[SDAChess]

Summary

Run the existing tmachine Kubernetes conformance scenarios on Kubernetes 1.29, OpenShell's documented minimum, instead of 1.36. Retry the startup readiness check because kubectl wait fails immediately when the Node has not registered yet, even with a readiness timeout.

Related Issue

Related to #2019. This PR covers the test cluster version and readiness check; the kube dependency upgrade remains separate.

Changes

• Pin the shared ubuntu-k3s setup to 1.29.15+k3s1, covering single-gateway and HA conformance runs.
• Retry the existing Node readiness task until it succeeds, retaining its 120-second readiness timeout.

Testing

• Ansible playbook syntax check passes.
• git diff --check passes.
• Fresh local KVM setup passes with the readiness retry change.
• nix run .#tmachine -- test ubuntu-k3s k3s conformance passes locally using matching CI artifacts; the guest reports v1.29.15+k3s1.
• Single-gateway and HA conformance CI lanes pass on the updated commit (test:e2e).

Checklist

• Follows Conventional Commits.
• Commits are signed off (DCO).

[github-actions]

Label test:e2e applied for b719196. Open the existing run and click Re-run all jobs to execute with the label set. The run will execute the standard E2E suite after building the required gateway, sandbox, and supervisor images once. The matching required CI gate status on this PR will flip green automatically once the run finishes.

[elezar]

Is there a reason that we chose 1.29? k8s offers around 1 year of patch releases and the oldest supported release is currently v1.34.

https://kubernetes.io/releases/

I understand that the documentation mentions v1.29, but I would rather change the documentation to mention the k8s support cadence instead of committing to supporting such an old version.

[SDAChess]

Is there a reason that we chose 1.29? k8s offers around 1 year of patch releases and the oldest supported release is currently v1.34.

https://kubernetes.io/releases/

I understand that the documentation mentions v1.29, but I would rather change the documentation to mention the k8s support cadence instead of committing to supporting such an old version.

I think changing that is out of the scope of this PR. I just want to be able to test my changes on our minimal documented support. Maybe worth opening a separate issue to discuss this.