Run a scheduled job now

Requests one of the live version's declared cron paths on this space's default hostname, right now, and returns what it answered. Requires write access to the space, because a cron handler can mutate state — the same authority wp-cli and db console require. target is a declared key or path — anything else is rejected, and no request is made. Headers are not passed through and redirects are not followed; use sf crons run --header for a handler that checks a secret. The platform's x-spacefast-cron header is never carried, so a handler gated on it will refuse.