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_

Reproduce the issue in a Windows Quick Chat session using plan mode, then inspect how the canvases pane is populated for repository-scoped sessions versus Quick Chat. The fix is complete when a plan canvas appears and can be viewed or commented on after an AI agent creates a plan in Quick Chat; verify the existing reproduction steps.

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