v0.4.0-next.4

setMe state now rides broadcast (reserved ~me event, throttled full-state, fire-and-forget) while presence carries membership only. Fixes frozen cursors + status flapping with 3+ people: Supabase presence is a low-frequency CRDT and stopped acking tracks within a second at cursor rates, while the identical load over broadcast sustained 97-100% delivery. Send rate now also scales down with room size instead of saturating the channel.