Backend-only re-cut of the #76 availability work onto main, stacked on the
canonical Weekend Context API. Adds request-scoped freshness reporting so
aggregate responses cannot report fresh when a component is stale, plus
local-first driver summary resolution and cache/pacing truth.
The frontend half of #76 is deliberately excluded: it is built on the
Weekend shell that failed owner review, including the full-width Partial
banner treatment. Availability presentation is re-cut with the shell in #89.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Add deterministic server-side chapter detection for starts, flag periods, pit phases, decisive top-five swings, and finishes, then expose chapters on the race-hub payload.
Spike result: race-hub already loads race control, positions, and laps in one read model. The requested Detect signature does not include pit stops, so pit phases use IsPitOutLap clusters as the local deterministic pit-stop proxy.
