No Plan canvas when using "Quick Chat"

### Short summary

No plan canvas when planning in quick chat

### Affected version or release

v0.2.27

### Installation context

Windows PC

### What happened?

When using plan mode in a quick chat to set up a new repository there was no canvas to view or comment on the plan this is something I rely heavily on and for quick chat it just wasn't there and there was sort of a general lack of canvases that were available in quick chat but most most notably was the plan canvas so I couldn't really view my plan like I can from sessions out of a repository.

### Steps to reproduce

1. Open "Quick Chat" session in the app
2. Switch to plan mode in the session text box
3. Create a plan with an AI agent
4. open the canvases pane on the left

### Expected behavior

There would be a plan canvas similar to planning sessions for repository-scoped sessions

### Additional context

_No response_

在使用 plan mode 的 Windows Quick Chat 会话中重现该问题，然后检查对于 repository-scoped sessions 和 Quick Chat，会如何填充 canvases 窗格。当 AI agent 在 Quick Chat 中创建计划后出现 plan canvas，并且可以查看或评论该画布时，修复即完成；请验证现有的重现步骤。

由索引模型根据 Issue 内容生成。