Add a button to displa current canvases available and run them

### Feature summary

Be able to relaunch extensions to ensure they are running

### What problem are you trying to solve?

When coming back to a session, extension is not running so my canvases are blank. I want to be able to run them from a button without prompting it.

### Proposed solution

Button to see extensions and relaunch them.

### Workflow impact

_No response_

### Installation context

_No response_

### Additional context

_No response_

Start by locating the desktop app’s existing canvas and extension UI, then trace how extensions are currently relaunched and prompted. Define the button’s expected list and behavior before implementing it; done means users can see available canvases or extensions and relaunch them without an additional prompt.

索引モデルが issue の本文から書いたものです。