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- Outdated comments should be resolvable too, instead of just `delete thread`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.

Start in the Changes view and reproduce each of the four reported workflows: file filtering, resolving comment threads, handling outdated comments, and locating new agent responses. Read the surrounding Changes view behavior before choosing scope. Done means the selected workflows are easier to use and each requested interaction behaves consistently.

Written by the indexing model from the issue text.