fix: use privileged k8s-runner docker

[casey-brooks]

Summary

• Switch the bootstrap k8s-runner Docker capability implementation from rootless to privileged.
• Label the agyn-workloads namespace for privileged Pod Security Admission enforcement, audit, and warn levels.

Closes #501

Tests

• terraform fmt -check -recursive — passed
• terraform -chdir=stacks/apps init -input=false && terraform -chdir=stacks/apps validate — passed
• terraform -chdir=stacks/platform init -input=false && terraform -chdir=stacks/platform validate — passed
• terraform -chdir=stacks/apps plan -refresh=false -input=false -lock=false — passed with local stub state/kubeconfig for remote-state inputs
• terraform -chdir=stacks/platform plan -refresh=false -input=false -lock=false -target=kubernetes_namespace_v1.agyn_workloads — passed with local stub state/kubeconfig for remote-state inputs; full platform plan requires a live Kubernetes API for kubernetes_manifest schema discovery

[casey-brooks]

Test & Lint Summary

• terraform fmt -check -recursive — passed (0 formatting issues)
• terraform -chdir=stacks/apps init -input=false && terraform -chdir=stacks/apps validate — passed (configuration valid)
• terraform -chdir=stacks/platform init -input=false && terraform -chdir=stacks/platform validate — passed (configuration valid)
• terraform -chdir=stacks/apps plan -refresh=false -input=false -lock=false — passed with local stub state/kubeconfig for remote-state inputs (Plan: 15 to add, 0 to change, 0 to destroy)
• terraform -chdir=stacks/platform plan -refresh=false -input=false -lock=false -target=kubernetes_namespace_v1.agyn_workloads — passed with local stub state/kubeconfig for remote-state inputs (Plan: 1 to add, 0 to change, 0 to destroy)

Full stacks/platform plan was not used because this stack contains kubernetes_manifest resources that require live Kubernetes API discovery; the targeted namespace plan verifies the changed PSA-label resource locally.

[noa-lucent]

Reviewed the Terraform changes against #501. The k8s-runner Docker capability now defaults to privileged, and the agyn-workloads namespace is labeled for privileged Pod Security Admission. Terraform fmt and validate pass after provider initialization. No changes requested.