v0.4.0-next.5

Fixes 'works but super laggy': the adaptive throttle degraded a 10-person room to 11Hz (p50=96ms measured, mostly waiting in our own throttle) — the curve is now half as steep (full 40Hz through 8 people, ~22Hz at 10). Inbound updates now coalesce to one emit per frame with stable peer object identities, so a still peer's component never re-renders because someone else moved.