Expose --salvage-only and --salvage-before-scrape on run-operator-validation.sh
and --salvage-before-scrape on run-operator-proof.sh so operators can merge stale
.dce-temp exports before or instead of incremental Discord scrapes.
Fail fast when archive or repo paths lack free space (DCE_MIN_FREE_MB),
treat disk-full export failures as skippable channels, and add an offline
disk-space smoke. Smokes default DCE_MIN_FREE_MB=0 so CI stays portable.