check_model_ladder: unarmed cells judge is not_measured on the nightly full ladder (#4667) #5192

Tracking issue for the minimal change on #4667.

The cells judge in scripts/lib/model_ladder_cells.py prints NOT ARMED and returns 0 when no required receipt carries a cells block. The release path never reaches that judge: with the standing release policy applying, check_model_ladder.sh judges the CRUX-smoke scope and exits first. Only the nightly's full ladder (--scope none, models-nightly models-ladder) reaches it, and there a quiet rc 0 means the cells row is never measured and never ticketed.

Change:

• Under --scope none only, an unarmed cells judge prints not_measured cells: ... and returns 1. The nightly row goes red, and --tickets opens its issue (LAB: the nightly job blocks nothing).
• Every other caller keeps rc 0.
• Case rows: red-cells-unarmed-nightly / green-cells-unarmed-not-nightly, plus two scope e2e rows proving a policy-covered release never reaches the cells judge and --scope none does.
• Mutants: unarmed-quiet, nightly-quiet, scope-falls-through.

Refs #4667