test: styled-system 지워보기

Author: halionaz

package-lock.json

@@ -18,7 +18,6 @@
     "@stackflow/plugin-history-sync": "^1.7.1",
     "@stackflow/plugin-renderer-basic": "^1.1.13",
     "@stackflow/react": "^1.5.2",
-    "@styled-system/css": "^5.1.5",
     "@tanstack/react-query": "^5.79.0",
     "axios": "^1.9.0",
     "react": "^19.1.0",