Improvements for `Changes` view

The `Changes` view is great for viewing the diffs. But it is missing some features:

- Filter files, like the GH webui allows you to do
- A way to collapse/resolve all the resolved comments being discussed locally.
- Outdated comments should be resolvable too, instead of just `delete thread`
- When sending multiple messages to the agent from the `Changes` view, and the responses are being posted - there is no easy way to see the new responses posted. You have to instead scroll around to find them. Or you look for strings like `response posted ..` in the agent chat window.

从 Changes view 开始，复现报告中的四个工作流：文件筛选、解决评论线程、处理过时评论，以及查找新的 agent 响应。在确定范围之前，先了解 Changes view 周边的行为。选定的工作流更易于使用，并且每个所要求的交互都表现一致，即视为完成。

由索引模型根据 Issue 内容生成。