Think组件可以自定义配置思考完成后是否自动折叠

**What problem does this feature solve? (这个功能解决了什么问题)**
思考过程流式输出，思考完成后自动折叠，避免思考过程太长，影响用户观感

**Describe the solution you'd like (描述您想要的解决方案)**

**What does the proposed API look like? (你期望的 API 是怎样的)**
Think组件增加一个collapsed属性，为true时，思考完成后自动折叠思考内容，为false时，思考完成后思考内容是打开的。

Start at the Think component entry point and inspect how it handles completion and content collapse. Add the collapsed configuration described in the issue, then verify that true folds the content after thinking completes and false leaves it open; no specific test file is named.

Written by the indexing model from the issue text.