fix(ui-migration): 显式校验源数据顶层数组键，禁止静默兜底

添加 readArray() 辅助函数，对四处顶层数组键 (ObjectList, ImageFileList,
LayerList, GroupList) 显式校验，缺失或非数组时即刻抛 SourceError，
不再用 ?? [] 蒙混。遵循 CLAUDE.md 第二准则：数据缺失/非法一律显式暴露。

新增四个测试用例分别验证各键缺失时的错误行为。删除测试文件中未使用的
mkdirSync 导入。条目级缺省值 (entry.Event ?? {}, ObjectList ?? []) 保留,
因为单个对象/层没有事件/对象是合理的合法缺省。

真实数据护栏数字不变: 991 对象 / 55 界面 / 80 组 / 439 图 / 139 多帧图。

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

cocoscreator_projects/scripts/test/ui-source.test.mjs

@@ -1,7 +1,7 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
 import { join } from 'node:path';
-import { mkdtempSync, mkdirSync, writeFileSync, rmSync } from 'node:fs';
+import { mkdtempSync, writeFileSync, rmSync } from 'node:fs';
 import { tmpdir } from 'node:os';
 import { ROOT } from '../lib/paths.mjs';
 import { loadSource, SourceError } from '../ui-migration/gameabc-source.mjs';
@@ -67,6 +67,50 @@ test('loadSource 对缺失文件显式抛错', () => {
   } finally { rmSync(dir, { recursive: true, force: true }); }
 });
 
+test('loadSource 缺少顶层数组键 ObjectList 时显式抛错', () => {
+  const dir = fakeSource({
+    'gameabc_Object.json': { Property: [] }, // 缺 ObjectList
+  });
+  try {
+    assert.throws(() => loadSource(dir), SourceError);
+    assert.throws(() => loadSource(dir), /ObjectList/);
+    assert.throws(() => loadSource(dir), /gameabc_Object\.json/);
+  } finally { rmSync(dir, { recursive: true, force: true }); }
+});
+
+test('loadSource 缺少顶层数组键 ImageFileList 时显式抛错', () => {
+  const dir = fakeSource({
+    'gameabc_Image.json': { id: 1 }, // 缺 ImageFileList
+  });
+  try {
+    assert.throws(() => loadSource(dir), SourceError);
+    assert.throws(() => loadSource(dir), /ImageFileList/);
+    assert.throws(() => loadSource(dir), /gameabc_Image\.json/);
+  } finally { rmSync(dir, { recursive: true, force: true }); }
+});
+
+test('loadSource 缺少顶层数组键 LayerList 时显式抛错', () => {
+  const dir = fakeSource({
+    'gameabc_Layer.json': { Property: {} }, // 缺 LayerList
+  });
+  try {
+    assert.throws(() => loadSource(dir), SourceError);
+    assert.throws(() => loadSource(dir), /LayerList/);
+    assert.throws(() => loadSource(dir), /gameabc_Layer\.json/);
+  } finally { rmSync(dir, { recursive: true, force: true }); }
+});
+
+test('loadSource 缺少顶层数组键 GroupList 时显式抛错', () => {
+  const dir = fakeSource({
+    'gameabc_GroupList.json': { data: [] }, // 缺 GroupList
+  });
+  try {
+    assert.throws(() => loadSource(dir), SourceError);
+    assert.throws(() => loadSource(dir), /GroupList/);
+    assert.throws(() => loadSource(dir), /gameabc_GroupList\.json/);
+  } finally { rmSync(dir, { recursive: true, force: true }); }
+});
+
 test('loadSource 在真实源数据上得到已知规模（回归护栏）', () => {
   const s = loadSource(REAL_SOURCE);
   assert.equal(s.objects.size, 991, '对象总数');