Add BreadClient::command (unsourced bread.command.<app>.<verb> emit) plus
health/api_version, and a clap-free screenshot_cli helper for the next pin.
get.sh now dies if minisign or .minisig is missing — checksum-only is not
enough to install. Generate the README products table from the registry,
and refresh release-channels/CONTRIBUTING/CLAUDE.md to match.
