Support jj instead of git

### Feature summary

Add first class support for jj

### What problem are you trying to solve?

Use jj as a first class tool with CoPilot

This brings good workspaces (better than worktrees), evolog (how a revision changes with each snapshot - great for undoing or understanding an agentic change), op log (giving the agent an ability to understand the source control changes over time), undo / redo (rather than just a revert), no staging area (because every revision is a staging are), etc.

### Proposed solution

jj native support in tool

### Workflow impact

This would be magic.

### Installation context

_No response_

### Additional context

_No response_

该 issue 没有指出任何文件、测试或入口点。首先定位应用现有的 Git 集成，并记录必须支持的 jj 工作流，包括 workspaces、snapshots、操作历史、undo、redo，以及不存在 staging area；当 jj 能够作为一流的源代码管理工具，并且这些工作流都已定义和验证时，即视为完成。

由索引模型根据 Issue 内容生成。