Closes#33548. `gateway.profile_routes` could only discriminate on where a
message came from (guild/channel/thread), so giving two people in one shared
chat their own isolated profile meant running two bots. Add `user_id` as a
route discriminator, conjunctive with the existing location fields and
matched on exact equality.
Kanban notifications revalidate a subscription's route before delivering, so
they pass the persisted sender too; a legacy subscription with no sender
identity falls back to the route's own `user_id` rather than skipping a route
that could have won, keeping the notify path fail-closed.
Cron is deliberately left out: it has no authenticated inbound sender, so a
`user_id` route never qualifies a cron delivery target. Operators need a
location-only route for that, which the docs now state.
d6f3285b81