feat(traps): activation VFX/SFX, explosion effect, and help section

Wire mimic/pit/arrow/laser media on activate, poison/explosion via effects, and document the scene editor and traps in Instructions.

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

app/renderer/shared/PresentationView.tsx

@@ -3,6 +3,7 @@ import React, { useEffect, useRef, useState } from 'react';
 import { computeTimeSec } from '../../main/video/videoPlaybackStore';
 import type { SessionState } from '../../shared/ipc/contracts';
 
+import { ExplosionVideoOverlay } from './effects/ExplosionVideoOverlay';
 import { PixiEffectsOverlay } from './effects/PxiEffectsOverlay';
 import { SceneDarknessOverlay } from './effects/SceneDarknessOverlay';
 import { useEffectsState } from './effects/useEffectsState';
@@ -169,6 +170,9 @@ export function PresentationView({
           }
         />
       ) : null}
+      {showEffects && scene?.previewAssetType !== 'video' ? (
+        <ExplosionVideoOverlay state={fxState} viewport={contentRect} />
+      ) : null}
       {scene?.previewAssetType === 'image' && contentRect ? (
         <SceneTrapsOverlay
           traps={scene.traps ?? []}
@@ -186,9 +190,9 @@ export function PresentationView({
             embedded
             assetId={activeMaterial.assetId}
             layout={materialsOverlay?.layout ?? DEFAULT_MATERIALS_OVERLAY_LAYOUT}
-            legendMarkers={
-              activeMaterial.legend?.enabled ? (activeMaterial.legend.markers ?? []) : undefined
-            }
+            {...(activeMaterial.legend?.enabled
+              ? { legendMarkers: activeMaterial.legend.markers ?? [] }
+              : {})}
           />
         ) : null}
         {activeMaterial?.legend?.enabled ? (