chore(io): migrate internal/cmd/setup to Medium abstraction
Migrated all direct os.* filesystem calls to use io.Local:
- cmd_repo.go: os.MkdirAll -> io.Local.EnsureDir, os.WriteFile -> io.Local.Write, os.Stat -> io.Local.IsFile
- cmd_bootstrap.go: os.MkdirAll -> io.Local.EnsureDir, os.Stat -> io.Local.IsDir/Exists, os.ReadDir -> io.Local.List
- cmd_registry.go: os.MkdirAll -> io.Local.EnsureDir, os.Stat -> io.Local.Exists
- cmd_ci.go: os.ReadFile -> io.Local.Read
- github_config.go: os.ReadFile -> io.Local.Read, os.Stat -> io.Local.Exists
Refs #116
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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