feat(tools): check-skin 独立校验 CLI

脱离构建即可自检 override, 秒级反馈; 有错退出码 1 并逐条指出
子游戏名+文件路径+原因(第二准则: 错误早暴露、可定位)。

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

cocoscreator_projects/package.json

@@ -9,6 +9,7 @@
     "new-game": "node scripts/new-game.mjs",
     "check-cocos": "node scripts/check-cocos-version.mjs",
     "bump-cocos": "node scripts/bump-cocos.mjs",
+    "check-skin": "node scripts/check-skin.mjs",
     "test:framework": "node scripts/run-framework-tests.mjs",
     "typecheck:framework": "tsc -p tsconfig.framework.json --noEmit"
   },