GET /api/dashboard/snapshot is additionalProperties: false in the spec
but the runtime emits three blocks the schema never declared: the
band/target math (targetBands, always present), the score-card
narrative (healthScore.tension / healthScore.returnToBand, additive
optional fields), and the briefing recall/forward-look
(briefingMemory). A strictly generated client rejects the real
response as a result.
Adds all four to dashboardSnapshotResponse with the exact runtime
type, optionality, and nullability, matching DashboardSnapshot in
src/lib/dashboard/snapshot.ts and the DTOs in
src/lib/dashboard/score-narrative.ts. No route behaviour changes.