Read path is cgo like search. Control questions live in rank so CI can
test them without ladybug. Python bin/kb/{get,stats,eval} stays the
runner fallback.
Commands live at bin/brain/{index,get,stats,eval,watch}.go and
bin/mail/import.go, bin/markdown/import.go, bin/postgres/query.go.
Python remains the Ladybug write worker. index_mail is a deprecation
shim that rebuilds via --with-mail.