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_

The issue names no files, tests, or entry points. Start by locating the app's existing Git integration and documenting the jj workflows that must be supported, including workspaces, snapshots, operation history, undo, redo, and the absence of a staging area; done means jj can serve as a first-class source-control tool with those workflows defined and verified.

Written by the indexing model from the issue text.