UnitSelectionEvent now forwards to view.setSelectedUnit(unit.id()) in
mountWebGLDebugRenderer; the renderer's SelectionBoxPass draws the
animated stippled outline on the GPU. UILayer still tracks
selectedUnit for game-logic readers (the click handlers) but no longer
paints to canvas2D for it.
Drops drawSelectionBox + lastSelectionBoxCenter (~50 LOC) plus the
per-tick single-unit redraw in tick(). Multi-selection stays on
canvas2D — SelectionBoxPass is single-unit only.
Test update: replaces the now-dead drawSelectionBox spy with a
selectedUnit state assertion + a deselect case.
evanpelle
ede0fb7668