fix: 修复迁移后的基础UI显示问题

app/lib/src/game/level.dart

@@ -59,7 +59,12 @@ class Entity implements EntityView, CamZoneLike {
   double speed = 2.4;
   int timer = 0;
   String kind = 'ball';
-  String? doorId;
+  // 与 web 原版一致：doorId 既可来自 data.doors[].id（常为 String），
+  // 也可在无匹配门时回退到实体序号 idx（int）。JS 弱类型下二者都能用 === 比较；
+  // 移植到 Dart 后若声明为 String?，回退分支把 int 赋给 String? 会抛
+  // "type 'int' is not a subtype of type 'String?'"。故用 Object? 容纳两种类型，
+  // == 比较（world.dart）对 String/String、int/int 走值相等，语义与 web 一致。
+  Object? doorId;
   int pair = 0;
   dynamic to;
   int cool = 0;
@@ -252,7 +257,8 @@ class Level implements LevelLike {
       }
       if (type == 'warp') {
         final cfg = (idx < warpSrc.length ? warpSrc[idx] : {}) as Map? ?? {};
-        final door = (data['doors'] as List?)?.cast<Map>()
+        final doors = (data['doors'] as List?)?.cast<Map>() ?? const <Map>[];
+        final door = doors
             .firstWhere((d) => d['tx'] == tx && d['ty'] == ty, orElse: () => <String, dynamic>{});
         e.doorId = (door != null && door.isNotEmpty) ? door['id'] : idx;
         e.pair = cfg['pair'] ?? (idx % 2 == 0 ? idx + 1 : idx - 1);