delete Pixi build-ghost rendering from StructureIconsLayer

The WebGL ghost (StructurePass + RangeCirclePass + RailroadPass +
CrosshairPass) is fed via GhostPreviewUpdatedEvent and looks correct;
the Pixi-rendered ghost was a duplicate.

Strip the Pixi side out of StructureIconsLayer:
- delete imports for pixi.js / pixi-filters / colord plugins / Theme /
  SpriteFactory / StructureDrawingUtils / bitmapFont / renderNumber
- delete fields: pixicanvas, ghostStage, rootStage, renderer,
  rendererInitialized, theme, factory, filterRedArray, rebuildPending,
  and the Pixi half of ghostUnit (container, priceText, priceBg,
  priceGroup, priceBox, range, rangeLevel, targetingAlly) — now just
  { buildableUnit }
- delete methods: setupRenderer, redraw, rendererOrGLContextLost,
  resizeCanvas, renderLayer, shouldTransform, updateGhostPrice,
  updateGhostRange, plus the Pixi guts of moveGhost /
  createGhostStructure / clearGhostStructure

init() is now sync; the per-RAF state checks move to a tick()-driven
syncGhostState() + renderGhost() (renderGhost still re-queries
buildables, just no longer paints anything).

Net: ~250 LOC gone, no canvas2D drawing left in the layer. The
canvas2D map canvas itself has no remaining writers — ready to be
deleted in a follow-up.

src/client/ClientGameRunner.ts

@@ -39,6 +39,7 @@ import {
   DoGroundAttackEvent,
   DoRequestAllianceEvent,
   DoRetaliateAttackEvent,
+  GhostPreviewUpdatedEvent,
   InputHandler,
   MouseMoveEvent,
   MouseUpEvent,
@@ -346,6 +347,12 @@ function mountWebGLDebugRenderer(
     view.showMoveIndicator(tx, ty, firstUnit.owner().smallID());
   });
 
+  // Build-mode ghost preview: forward the per-frame state to the renderer's
+  // ghost passes (structure outline, range circle, rail snap, crosshair).
+  eventBus.on(GhostPreviewUpdatedEvent, (e) => {
+    view.updateGhostPreview(e.data);
+  });
+
   // Warship selection boxes: forward UnitSelectionEvent to the renderer's
   // SelectionBoxPass for both single and multi selections.
   eventBus.on(UnitSelectionEvent, (e) => {