upload per-fixture iso render for the leaderboard gallery

dockerfile: pin cadgenbench to f90bbc5 (render-pool hang fix); deterministic rebuild

dockerfile: build cadgenbench from main with commit-endpoint cache-bust

readme: explicit paused image-only Space framing

dockerfile: bootstrap pip for python 3.12 via ensurepip

initial commit: Dockerfile + eval_job.py + README

initial commit