[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
```

从处理所选 Remote 分支的工作区创建流程开始，跟踪传递给 git checkout -B 命令的值。使用仅存在于 Remote 上的分支（例如 master-updated-stu）重现，然后验证使用远程跟踪引用可以成功创建工作区，并且生成的工作区基于所选的 commit。

由索引模型根据 Issue 内容生成。