Bare operations so that this work with jujutsu, etc.

I'm using jujutsu so please provide commands that does not create any branch, checkout any branch, etc.
For comparison, graphite has `--branch` arg for essential commands so it can work with jujutsu.

I'll even question why it isn't designed like this. Like you only need
`gh stack `: Stack `branch1` on top of `branch2`, or if branch2 is missing, it will be the first branch in the stack
`gh submit `: Push a tracked branch to github.

先檢視現有命令的行為，以及 issue 中描述的 jujutsu 與 Graphite 比較。定義哪些操作必須避免建立分支或 checkout，接著釐清提議的命令介面，以及缺少第二個分支和提交受追蹤分支時的行為。

由索引模型根據 Issue 內容生成。