Pls give us option to disable worktrees globally in settings.

### Feature summary

_No response_

### What problem are you trying to solve?

When I start a new session in a folder that has 40 repos (welcome to my world), It's really annoying to have to specify 40 branches, and toggle 40 worktree toggle's off. And even when they are off, it still creates worktrees.

### Proposed solution

Global setting to turn off all worktree related stuff. (this toggle should also leave the branches as they were)

### Workflow impact

This would massively help people who don't need worktrees.

### Installation context

_No response_

### Additional context

GitHub CoPilot Desktop app v1.0.25

Start by locating the app settings and the session setup path that creates worktrees across repositories. Confirm how per-repository worktree toggles and branch selection are applied. Done means a global setting disables worktree creation and leaves existing branches unchanged across all repositories.

Written by the indexing model from the issue text.