- Define pool.FileSystem interface in internal/io/pool/filesystem.go
- Move DirEntry interface to internal/io/pool/types/types.go to break
the pool <-> mock import cycle
- Implement real.FileSystem with atomic writes (temp file + os.Rename)
- Update mock.FileSystem to satisfy pool.FileSystem interface
- Update worker pool tasks to accept pool.FileSystem interface
- Update main.go to use RealFileSystem by default, with -root flag
- Update all browser/editor/test references to types.DirEntry
