Find duplicate files with safe command-line scanner

Build a dependency-free Node.js command-line tool that recursively scans one user-supplied directory and reports groups of byte-identical regular files. It must never delete, rename, or write to scanned files. Skip symbolic links and .git directories, handle empty files, compare candidate files by size then streaming SHA-256 and finally bytewise confirmation so each reported group truly contains identical bytes. Produce deterministic JSON on stdout with sorted paths and groups, including duplicate byte savings. Give clear usage/help and nonzero exit for invalid or unreadable root. Continue scanning on individual unreadable entries with warnings on stderr. Add a small fixture or example and Node built-in tests using temporary directories for identical content, equal size but different content, empty files, symlinks, deterministic ordering, and error behavior. Include README with exact commands and safety notes.