期望：appendMsg后不强制滚动到底部

**What problem does this feature solve? (这个功能解决了什么问题)**
每次调用appendMsg插入新消息时，都会强制滚动到底，如果A用户在看消息时候，突然B来了新消息，就会滚到底部影响原有的查看逻辑

**Describe the solution you'd like (描述您想要的解决方案)**
期望暴露一个属性配置，允许发送消息后不自动滚动

**What does the proposed API look like? (你期望的 API 是怎样的)**

Start by locating the appendMsg implementation and the code that performs automatic scrolling after a new message. Review how message insertion and scroll behavior are tested, if tests are present. Done means an exposed configuration option can disable automatic scrolling after appendMsg while preserving the current default behavior.

Written by the indexing model from the issue text.