body { overflow: hidden; } in dist/index.css prevents page scrolling

**Version information (版本信息)**
- ChatUI or ChatUI Pro? ChatUI
- ChatUI Version: 3.0.0
- React Version: 19.1.0
- OS Version: macOS 15.3
- Browser Version: Chrome 134.0.6998.118

**Describe the bug (描述问题)**
In @chatui/core v3, the bundled stylesheet (dist/index.css) includes a global rule:
body {
margin: 0;
overflow: hidden;
}
This causes the entire page to become unscrollable whenever the package is loaded.

**Expected behavior (期望的结果是什么)**
The ChatUI stylesheet should not apply overflow: hidden to the global element. Page scrolling should remain functional. Ideally the overflow rule should be scoped only to the ChatUI container.

Start by tracing the source that produces dist/index.css and inspect the global body rule shown in the issue. Verify that the bundled stylesheet no longer prevents page scrolling while the ChatUI container retains any required overflow behavior.

Written by the indexing model from the issue text.