fix(animation): WASM 모드 안정성 개선

- SchedulerBinding으로 프레임 빌드 중 setState 방지
- persistentCallbacks 단계에서 addPostFrameCallback으로 지연 처리

lib/src/features/new_character/widgets/race_preview.dart

@@ -1,6 +1,7 @@
 import 'dart:async';
 
 import 'package:flutter/material.dart';
+import 'package:flutter/scheduler.dart';
 
 import 'package:askiineverdie/src/core/animation/character_frames.dart';
 import 'package:askiineverdie/src/core/animation/race_character_frames.dart';
@@ -48,7 +49,19 @@ class _RacePreviewState extends State<RacePreview> {
 
   void _startAnimation() {
     _timer = Timer.periodic(const Duration(milliseconds: 400), (_) {
-      if (mounted) {
+      if (!mounted) return;
+
+      // 프레임 빌드 중이면 다음 프레임까지 대기 (WASM 모드 안정성)
+      if (SchedulerBinding.instance.schedulerPhase ==
+          SchedulerPhase.persistentCallbacks) {
+        SchedulerBinding.instance.addPostFrameCallback((_) {
+          if (mounted) {
+            setState(() {
+              _currentFrame++;
+            });
+          }
+        });
+      } else {
         setState(() {
           _currentFrame++;
         });