feat: brain/index.go shebang; mail import is not a brain write (D14). (#12)

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.

bin/mail/sync.go

@@ -6,7 +6,7 @@
 //	./bin/mail/sync.go --dry-run
 //
 // Writes raw message.json + attachments under var/mail/<folder>/<id>/; run
-// bin/mail/import --from-raw afterwards to convert everything to markdown.
+// bin/mail/import.go --from-raw afterwards to convert everything to markdown.
 //
 // Shebang trick: first line is a Go `//` comment; the real code lives in the
 // importable package (module path, never a relative import).