Create per-user git worktrees

[AndreFavotto]

Create a temporary git worktree for each developer user making changes.
After that, get_staging_repo API method should always return the path to the worktree env.
After user commits their changes, the git worktree should be cleaned up.

This will prevent users from simultaneously editing the same files.

For the demo developer a different strategy will need to be thinked of: since it is a shared user, worktrees cannot be user-based. First idea is to use browser-based worktrees via UUID saved in browser localStorage.