Option to open right sidebar as separate window

### Feature summary

Sidebars as separate windows

### What problem are you trying to solve?

Feature request:
Sometimes it would be very useful, if the right (panels) sidebar could be opened in a **new window**. This would also give some extensive canvases more realestate. All tabs (like Changes, Terminal, Insights, ...) should remain in this new window, same as now in the sidebar.

---
| Field | Value |
| --- | --- |
| App version | 1.1.7 |
| OS | macOS 15.7.9 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Week 7 |

### Proposed solution

A new settings option, that toggles between "sidebar in main App window" and "sidebar as separate window"

If set to separate window, all tabs of current right sidebar appear in a new window of the running Copilot App

### Workflow impact

- Canvases have more realestate
- multi-display environments profit

### Installation context

_No response_

### Additional context

_No response_

未指定文件、测试或入口点。首先定位右侧边栏和设置的实现，然后确定所有列出的边栏标签页的独立窗口行为范围。完成标准是：通过一项设置，可以在主窗口的边栏和独立窗口之间切换，同时保留这些标签页，并为画布提供更多空间。

由索引模型根据 Issue 内容生成。