Copies a local jar under pack/custom/ (served by caddy), sha256s it,
writes pack/mods/<slug>.pw.toml per packwiz "Other external files",
then packwiz refresh. Cautious: halts on bad side, whitespace in
filename, or existing entry without --force.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
