Content-hash based dedup (size -> partial SHA-256 -> full SHA-256), not
filename matching, so identically-named files with different content are
never confused for duplicates and differently-named files with identical
bytes always are. Stdlib-only Python so it runs unmodified on Windows
10/11 and Debian-flavored Linux (Ubuntu, Mint). Supports photo/music/
video/docs extension categories or custom extensions, JSON/CSV reports,
and optional delete/move/hardlink cleanup actions that default to a dry
run and require --yes to actually touch files.
