fix(helm): restore Kubernetes e2e chart rendering

[drew]

Summary

Restore Kubernetes e2e Helm installs after #3677 left an empty supervisor.sandboxRuntime override in the Skaffold values file. Helm treated it as null and failed while rendering boundaryPort in gateway config, blocking the Kubernetes jobs on #3686 before tests could start.

Related Issue

No issue required: this is an obvious localized regression in the Helm CI values file introduced by #3677.

Changes

• Remove the empty supervisor.sandboxRuntime key and obsolete comment from the Skaffold values file so the chart's default boundaryPort remains available.
• Make helm:lint render the default chart and every CI values variant, catching template errors that helm lint alone misses.

Testing

• mise run pre-commit passes.
• mise run helm:lint passes and renders all CI values variants.
• mise run helm:test passes (187 Helm unit tests).
• mise run ci did not pass locally: the Go SDK gateway tests see this host's /etc/openshell/gateways/default system entry and fail assertions that expect only test-created gateways. The Helm checks above pass.
• Kubernetes e2e is requested through the test:e2e label; awaiting CI.

Checklist

• Follows Conventional Commits.
• Commit is signed off (DCO).
• Architecture docs reviewed; no architecture behavior changed.

[github-actions]

Label test:e2e applied for 292b0f3. 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.