[seanharding]

Before / After always compared the edit with the default conversion. Right-click a history step for Compare With This Step, or a work print for Compare With This Version, to put that version on the left of the split instead.

• The before half takes the version's look on the current geometry, composite, flat field and output settings, so both halves line up.
• The reference is held as a config, so a later edit that deletes the step keeps the comparison. Closing the split, Esc and a frame change drop it.
• The badge reads STEP N or the work print name. Picking a new reference while the split is open drops the old pixels and renders the new one.
• The preview is not decoded again, so a step's decode-time settings (demosaic, sensor unmix, highlight reconstruction) follow the current source.

Guide, ja/ko/zh_CN catalogs and the two History guide panels updated. Verified headless on a sample ORF: step 0, step 1 and a work print each render as the before half, with step 1 between step 0 and the current edit.