Challenges with collaborative usage across local instances

When a collaborator clones the repository, their local instance does not include the necessary git-spice configuration (e.g., branch stacks stored in `.git`). As a result, anyone else apart from me is unable to use git-spice commands to manage my stack without manually initializing or recreating the configuration.

### Example

I was using `gs` to manage a stack:

A colleague resolved a merge conflict on a PR with the trunk branch and pushed the changes. However, they couldn’t use `gs usr` to restack the dependent pull requests due to the absence of the git-spice configuration in their local instance. The colleague eventually merged the PR manually.

When I pulled the changes and ran `gs repo sync`, it got stuck, repeatedly prompting me to rebase the same commit. I had to:

- `untrack` all branches.
- Perform a git pull.
- `track` all branches in the exact same order.

This situation has occurred twice, so I can provide a reproducer if required.

### Issues
- `gs repo sync` did not work as expected and failed to recover the branch stack properly.
- `gs` did not work on my colleague's local instance because their configuration was not initialized. (I’m not sure if this is feasible given the current storage mechanism in .git.)

---

That said, good stuff on git-spice btw! It has become a daily driver :)