Add opt-in hardening to the agents-as-a-service example:
- commented runtimeClassName/nodeSelector fields for sandboxes and Deployments
- optional sandbox NetworkPolicy plus exposure-variant policies
- optional dsh-provider-keys-extra Secret for extra provider keys
- docs/optional-hardening.md with verification, caveats and rollback
The base walkthrough stays portable; no gateway code, routes or auth changed.
Co-authored-by: SREDevOpsAgents <agents@sredevops.org>