Replace hard-coded /cluster/home/morri313 image paths in cluster-render callers with a repo variable #1658

The cluster-render callers pass cluster-image: /cluster/home/morri313/ci/image/lds-ci.sif and cluster-image-file: /home/morri313/ci/image/lds-ci.sif as literals. Claude's reviews flagged this on dl#19, araomm#27 and career#11, and the coordinator reports the images now also live at /cluster/research-groups/morrison/ci/image/, so every caller needs the same edit.

Wanted: one org Actions variable (for example CI_CLUSTER_IMAGE) read by the callers, or a gha default, so the path changes in one place.

Callers affected: cv, career, dl, araomm, csci201, lds-new, demo2 and any other private repo calling preview.yml or quarto-publish.yml with cluster-render. Setting an org variable needs Ezra or the runner thread.

Posted by Claude Code (AI agent) --- not written by a human.