feat(operator): PSA-restricted securityContext for broker and etcd pods #163

Context

PR #152 hardens the four chart-templated Deployments (operator, proxy, console, mcp) for Pod Security Admission restricted. Brokers and managed etcd are operator-reconciled (app=kafscale-broker, etcd StatefulSet/Deployment), so they are out of scope for the chart change.

Task

Add PSA restricted-compatible pod and container securityContext defaults to operator-reconciled broker and etcd workloads, aligned with the shipped images (USER 10001).

Acceptance

• Broker and etcd pods render/run with the same restricted controls as chart workloads (runAsNonRoot, dropped capabilities, readOnlyRootFilesystem, seccompProfile: RuntimeDefault, etc.)
• Writable mounts added only where runtime code requires them (mirror proxy /tmp pattern if needed)
• Conformance test or operator render test prevents regression