When `Config.dev` is true, the operator typically registers slash
commands per-guild (Config.guildId) during iteration so they appear
instantly. Once those leak past dev, the same commands show up in
Discord twice — once from the dev guild registration and once from
the global registration.
Before doing the global PUT, also PUT an empty array against the
dev guild so any stale per-guild commands are cleared. Behavior in
production (Config.dev=false) is unchanged.
