Allow scrolling through the current conversation history

Describe the feature or problem you'd like to solve

● Describe the feature or problem you'd like to solve ┃ In Copilot CLI, using the mouse wheel or PageUp/PageDown navigates through prompt history instead of scrolling the ┃ current conversation. ┃ ┃ When the conversation becomes long, I cannot scroll up to review earlier messages at the top of the same ┃ conversation. This makes it difficult to refer back to previous requirements, responses, and context.

Proposed solution

Provide a way to scroll through the current conversation independently from prompt-history navigation.
Mouse-wheel scrolling and PageUp/PageDown should scroll the conversation view, while prompt-history navigation
should use separate configurable keybindings.

Example prompts or workflows

No response

Additional context

1. Have a long conversation with multiple prompts and responses.
2. Scroll upward to review messages from earlier in the same conversation.
3. Use PageUp/PageDown to move through the conversation history.
4. Use separate keys when navigating previously entered prompts.

从 Copilot CLI 中对 mouse-wheel 和 PageUp/PageDown 事件的输入与 conversation-view 处理入手。追踪这些按键当前如何浏览 prompt 历史，然后确定现有的按键绑定配置；完成的标准是，滚动操作能够查看当前对话中的较早消息，而 prompt 历史导航使用单独的可配置按键。