Gotcha 9: the resident tower is a cliff config even headless (#36 follow-up)

Re-verified the vision-offload premise on a headless 3090: VISION_OFFLOAD=0
does boot with nothing else on the card, but lands at 440 MiB free -- inside
gotcha 39 kill territory for a concurrent burst. The hard no-boot in #36 needs
a desktop compositor sharing the card, which the measuring box had. Offloaded
vs resident is full-margin vs cliff either way, so the default stays on.