- Add .repo.git as shared bare repo for worktrees
- Update polecat manager to use bare repo when available
- Add git.NewGitWithDir() and CloneBare() for bare repo support
- Update gt rig init to create bare repo architecture for new rigs
- Refinery and polecats now share branch visibility via shared .git
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>