Closes https://github.com/zed-industries/zed/issues/41094 This PR adds the `agent_buffer_font_size` settings to be scaled in the same proportion as the agent panel's UI font size, which was the only setting that was being accounted for. This is something that I forgot to do when we broke down the agent panel's font size controls into these two values. Release Notes: - agent: Fixed an issue where the agent panel's buffer and UI font size wouldn't scale proportionally.