v1.39.0 — Actionable disk warning

Changed

• Disk-space warning is now actionable (#2, @famewolf). A bare ⚠️ Disk usage at 88% — 5.3 GB free. used to get lost in the noise (famewolf's 215 GB-of-orphaned-images lesson: the warning did fire, he just glossed over it while wrestling with LLM disk pressure). The warning now tells you how much space /cleanup could reclaim (from docker system df — unused images / build cache) and, if DISK_WARN_AUTO_CLEANUP is OFF, a one-line nudge to turn it on. So the message becomes "🧹 21.3 GB reclaimable via /cleanup — auto-cleanup is OFF, set DISK_WARN_AUTO_CLEANUP=true to reclaim automatically next time." Hard to ignore.

Full 22-script regression sweep green.