Squirrel: the preview lists only what will move, and nothing shows above its header

Suite 2.246.10, Squirrel 1.31.0.

What changed

The list can show only the site folders that have files to move. After a folder is scanned and Show File Details is pressed, a Show control on the row with Check All, Uncheck All, Advanced and Apply Moves has two buttons: Moving only and Everything. Moving only is the default. It lists just the site folders with files to move, without the "Staying in root" tables, so a large folder no longer has to be scrolled to find the files the summary counts. A note beside the buttons says how many site folders are hidden. Everything lists every site folder and the files that stay, as before.
The choice is remembered and survives rescanning. Switching between the two does not redraw the list, so a file that was unchecked or given a different destination keeps that setting.
With Advanced on, a site folder with unreferenced images or floor plans stays in the list under Moving only, even when nothing in it will move.
If nothing will move, Moving only says so and points to Everything.
Rows no longer show above the header while scrolling. The bar with Change Folder, New Folder, Rescan and Settings, and the summary below it, now hold at the very top of the scroll area. Previously a strip of the list's top margin stayed above the bar, and file rows scrolled up through it.

A browser test in Firefox, Chrome and Edge scans an invented folder of forty sites with three files to move. It checks that the list opens on the two sites with moves, that Everything lists all forty, that an unchecked box stays unchecked after switching back and forth, that the choice survives a rescan, and that after scrolling the element at every point along the top edge of the list is the header. It fails when the hiding rule is removed and when the header is held at its old position.
The full suite passes.