Avoid fork PR head branch collisions when creating worktrees

- create a unique local branch name for cross-repo PR worktrees (`pr/<number>-<head>`)
- fetch/set upstream against that local branch instead of overwriting local `main`
- add regression tests for fork PRs where head branch is `main`
f7570712a7Julius Marminge committed on 3/10/2026, 5:50:45 AM· committed by Julius Marmingeparent2847655
2 files changedLine totals unavailable