The derived envelope types `value` as an open record, so the sleep
score's `rhythmNights` and per-sub-score `gap` were on the wire but in
no schema. `SleepScoreValue` joins `WellnessScoreValue` in the forced
components slot, the envelope's `value` description names it, and a
contract test holds the published field set to the one the engine
emits, for a scored rhythm and for one withheld for too few nights.
Refs #1204
