When using "-" to read paths from stdin, if stdin is empty or contains
only blank lines, return an explicit error instead of silently succeeding
with no work done.
filepath.Walk uses Lstat, so symlinks are reported with ModeSymlink set,
never ModeDir. The info.IsDir() check was always false, making the
filepath.SkipDir branch unreachable dead code.
- Add -q/--quiet flag to suppress all output except errors
- Add progress bar with 250ms refresh, file count, and ETA display
- Print summary report to stderr on completion (files processed, skipped, failed, bytes, duration)
- Support reading paths from stdin with "-" argument (e.g., find | attrsum sum add -)
- Update README with new features and updated TODO section
- Change sum add, sum update, check, and clear to accept 1+ paths
- Update README usage examples to show multiple path support
- Add TODO section with planned future improvements
