Show thumbs-up and thumbs-down feedback actions in Agent Host chats

## Description

When a chat uses Agent Host, assistant responses do not show the thumbs-up and thumbs-down feedback actions.

Response rating is a VS Code-level feedback surface and does not need to depend on capabilities exposed by a particular harness or provider. Selecting Agent Host should therefore not remove these controls.

## Expected behavior

Assistant responses rendered through Agent Host expose the same thumbs-up and thumbs-down feedback UI as other chat sessions, with VS Code handling the feedback independently of the selected harness.

## Actual behavior

The response feedback actions are missing when using Agent Host.