[Bug]: Remote branch selection uses an unresolved local branch name when creating a workspace

### Platform

Windows

### Operating system version

11

### System architecture

Windows

### PolyScope Version

0.26

### Bug description

Creating a workspace from a non-default branch fails even when I select that branch from the Remote branches section.

Polyscope appears to discard the remote qualification and passes the branch’s short name to git checkout -B. The new clone only contains the branch as a remote-tracking ref, so Git cannot resolve the supplied start-point.

Inspection of the failed clone shows:

```
refs/heads/master
refs/remotes/origin/master-updated-stu
```

The remote-tracking ref resolves successfully:

`git rev-parse --verify "origin/master-updated-stu^{commit}"`

But the short local name does not:

`git rev-parse --verify "master-updated-stu^{commit}"`
fatal: Needed a single revision

### Steps to reproduce

1. Open a repository whose default/current branch is master.
2. Ensure another branch, such as master-updated-stu, exists on origin.
3. Start creating a new workspace "from branch"
4. Search for or select relevant branch name.
5. Select the entry marked Remote.
6. Create the workspace.

### Relevant log output

```shell
Command failed: git checkout -B "brave-moth" "master-updated-stu"
fatal: 'master-updated-stu' is not a commit and a branch 'brave-moth' cannot be created from it
```

Start at the workspace creation flow that handles the selected Remote branch and trace the value passed to the git checkout -B command. Reproduce with a remote-only branch such as master-updated-stu, then verify that workspace creation succeeds using the remote-tracking reference and that the resulting workspace is based on the selected commit.

索引モデルが issue の本文から書いたものです。