ci: migrate GitHub Actions runners to k8s-personal (ARC ephemeral)

[BrewingCoder]

Summary

The Proxmox lab has been clustered and Actions Runner Controller (ARC) is now deployed on MicroK8s. All GitHub Actions should target the new K8s ephemeral runners.

Changes Required

Update runs-on from [self-hosted, Linux, holdfast] to k8s-personal across all workflow files.

Affected workflows:

• ci-backend.yml
• ci-frontend.yml
• ci-sdk.yml
• publish-npm.yml (5 jobs)
• security.yml (5 jobs)
• sonarqube.yml (3 jobs)

Benefits

• Ephemeral runners — clean environment every job (fixes past issues with corrupted build cache, page faults from stale state)
• Docker-in-Docker supported
• Scales to 0 at idle

[github-actions]

AI Triage: Migrate GitHub Actions runners from self-hosted Proxmox to Kubernetes-based ephemeral runners (ARC) across all workflow files.

Labels applied: area:ci, tech-debt, priority:medium