feat(scene): battle grid overlay with color and trap VFX stacking

Add configurable square/hex grid in the scene editor (persisted and shown on control/presentation) and keep trap activation effects above trap icons.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/renderer/control/ControlApp.tsx

@@ -35,6 +35,7 @@ import { NpcsSceneOverlay } from '../shared/npcs/NpcsSceneOverlay';
 import { useNpcsOverlayState } from '../shared/npcs/useNpcsOverlayState';
 import { SceneOverlayHost } from '../shared/sceneOverlay/SceneOverlayHost';
 import { useSceneViewState } from '../shared/sceneView/useSceneViewState';
+import { SceneGridOverlay } from '../shared/grid/SceneGridOverlay';
 import { SceneTrapsOverlay } from '../shared/traps/SceneTrapsOverlay';
 import { useSceneTrapsState } from '../shared/traps/useSceneTrapsState';
 import { Button } from '../shared/ui/controls';
@@ -1710,10 +1711,11 @@ export function ControlApp() {
             </div>
             {!isVideoPreviewScene ? (
               <>
+                <SceneGridOverlay grid={currentScene?.grid} viewport={previewContentRect} />
                 <PixiEffectsOverlay
                   ref={effectsOverlayRef}
                   state={fxState}
-                  style={{ zIndex: 1 }}
+                  style={{ zIndex: 6 }}
                   viewport={
                     previewContentRect
                       ? {