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/shared/effectEraserHitTest.ts

@@ -52,7 +52,8 @@ export function minDistSqEffectToPoint(inst: EffectInstance, p: { x: number; y:
     case 'scorch':
     case 'ice':
     case 'shadow':
-    case 'poisonCloud': {
+    case 'poisonCloud':
+    case 'explosion': {
       const dx = inst.at.x - p.x;
       const dy = inst.at.y - p.y;
       return dx * dx + dy * dy;
@@ -67,7 +68,8 @@ function eraseHitThresholdSq(inst: EffectInstance, toolRadiusN: number): number
     inst.type === 'scorch' ||
     inst.type === 'ice' ||
     inst.type === 'shadow' ||
-    inst.type === 'poisonCloud'
+    inst.type === 'poisonCloud' ||
+    inst.type === 'explosion'
   ) {
     const r = toolRadiusN + inst.radiusN;
     return r * r;