runpod: engines image on the light core — 2.4 GB instead of 9.1

The engines are C binaries and coderai only drives them; the full core's
torch was dead weight. All they link is the CUDA runtime and cuBLAS,
which NVIDIA ships as wheels at the 12.8 they were compiled against.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0182DhR1eFNPQyGmDrpHbedY