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/shared/PresentationView.tsx

@@ -9,6 +9,7 @@ import { SceneDarknessOverlay } from './effects/SceneDarknessOverlay';
 import { useEffectsState } from './effects/useEffectsState';
 import { useSceneDarknessState } from './effects/useSceneDarknessState';
 import { DEFAULT_MATERIALS_OVERLAY_LAYOUT, DEFAULT_NPCS_OVERLAY_LAYOUT } from '../../shared/types';
+import { SceneGridOverlay } from './grid/SceneGridOverlay';
 import { MaterialLegendPanel } from './materials/MaterialLegendPanel';
 import { MaterialOverlay } from './materials/MaterialOverlay';
 import { useMaterialsOverlayState } from './materials/useMaterialsOverlayState';
@@ -159,10 +160,22 @@ export function PresentationView({
       ) : (
         <div className={styles.placeholderBg} />
       )}
+      {scene?.previewAssetType === 'image' ? (
+        <SceneGridOverlay grid={scene.grid} viewport={contentRect} />
+      ) : null}
       <div className={styles.vignette} />
+      {scene?.previewAssetType === 'image' && contentRect ? (
+        <SceneTrapsOverlay
+          traps={scene.traps ?? []}
+          session={sceneTraps}
+          viewport={contentRect}
+          mode="presentation"
+        />
+      ) : null}
       {showEffects && scene?.previewAssetType !== 'video' ? (
         <PixiEffectsOverlay
           state={fxState}
+          style={{ zIndex: 6 }}
           viewport={
             contentRect
               ? { x: contentRect.x, y: contentRect.y, w: contentRect.w, h: contentRect.h }
@@ -173,14 +186,6 @@ export function PresentationView({
       {showEffects && scene?.previewAssetType !== 'video' ? (
         <ExplosionVideoOverlay state={fxState} viewport={contentRect} />
       ) : null}
-      {scene?.previewAssetType === 'image' && contentRect ? (
-        <SceneTrapsOverlay
-          traps={scene.traps ?? []}
-          session={sceneTraps}
-          viewport={contentRect}
-          mode="presentation"
-        />
-      ) : null}
       {showEffects && scene?.previewAssetType === 'image' && scene.darkenScene && contentRect ? (
         <SceneDarknessOverlay state={sdState} overlayAlpha={1} viewport={contentRect} />
       ) : null}