Toggle to hide tool call activity during streaming

### Describe the feature or problem you'd like to solve

Toggle to hide tool call activity during streaming

### Proposed solution

When the model uses tools, the UI shows intermediate activity like:
"Checking my documentation"
└ # GitHub Copilot CLI Documentation
"Running bash command"
└ ...

This is informative but noisy, especially for quick questions where multiple tools fire.

Request: Add a keybinding (e.g., Ctrl+T style) or /command to toggle between:
1. Show all tool activity (current default)
2. Show only final response text (hidden tool calls) + show in footer/status bar that call activity is hidden

The hidden view would still show the final answer — just hide the intermediate "working on it" indicators. Similar to how Ctrl+T toggles reasoning display.

### Example prompts or workflows

_No response_

### Additional context

_No response_

首先定位現有的 Ctrl+T 推理顯示切換開關，以及用於渲染串流工具活動的程式碼。實作完整活動與僅顯示最終回應的輸出之間的切換，在頁尾或狀態列中顯示隱藏狀態，並在使用工具的 prompt 期間驗證這兩種顯示模式。

由索引模型根據 Issue 內容生成。