Give the move-subject action an icon that is not the drag cursor

[JeroenDeDauw]

Follows-up to #1356

The Move action on the Data tab used cdxIconMove, the four-way arrow that is also the
browser's drag cursor, one button away from the row's drag handle in a list that is dragged to
reorder. A glyph that says "drag me" sat on the button that relocates a Subject to another page.

It now uses cdxIconArticleRedirect, a page with an arrow leading away from it: the
container-plus-arrow shape mail and file tools use for "move to", with a page as the container.
The dialog's confirm button and the overflow-menu entry carry the same icon, and the
ResourceLoader icon list follows.

Considered, omitted: a custom page-with-arrow glyph without the redirect association, and moving
the action into a labelled overflow menu on desktop.

_{AI-authored — Claude Code, Fable 5.1 (max); one-line ask from @JeroenDeDauw after an in-session icon discussion, no revisions; diff not yet human-reviewed; SubjectsManager vitest specs and eslint run locally, icon checked in the dev wiki, CI pending.}

[JeroenDeDauw]