fix(ui): vim selection reset only clears selections inside the viewer (#1608)

* fix(ui): vim selection reset only clears selections inside the viewer

useVimSelection cleared the whole page's selection on every Viewer mount and
contentVersion change while vim was off, killing selections made in other
panels of a host. Every reset now goes through clearSelectionWithin(container),
which only clears a selection whose anchor or focus lies inside the viewer.

Bumps @plannotator/ui to 0.46.1 (core pin unchanged).

* docs(ui): annotateParity shipped in 0.46.0