### Summary of Changes
- Evaluated `short_sha` inside a bash step (`id: vars`) so Docker
`build-args` receives the expanded short SHA (e.g. `sha-4429a65`) rather
than literal bash code strings.
- Added `- flux-system` to
`ci/k8s/clusters/production/kustomization.yaml` to prevent Flux from
pruning its own `GitRepository` resource during reconciliation.