SelectionBoxPass now stores an array of selections and renders one
quad per entry. GPURenderer gains setSelectedUnits(ids) — the
single-unit setSelectedUnit becomes a wrapper. Position + color are
rebuilt each frame from lastUnits; dead unit IDs get pruned in place.
ClientGameRunner's UnitSelectionEvent listener forwards both single
and multi to view.setSelectedUnits — no more single/multi split.
UILayer drops everything canvas2D-related: the offscreen canvas +
context, theme, selectionAnimTime, multiSelectionBoxCenters,
SELECTION_BOX_SIZE, drawSelectionBoxMulti, paintSelectionBoxAt,
clearSelectionBox, paintCell, clearCell, and renderLayer / redraw /
shouldTransform. tick() now only prunes destroyed warships from the
selection list; the layer is purely state + click handling. ~120 LOC
gone.
Tests: UILayer.test.ts updated — drops the canvas/redraw asserts,
adds a multi-selection state assertion.
evanpelle
923cba8c2d