Address PR #82 review blockers: drop the competing /weekend
default_analysis_session resolver, land bare /race-hub via
/api/v1/weekend-context, derive Live/preparing/partial/unavailable from
authoritative context with a moving clock, hide Local Coverage behind
Diagnostics, isolate the future-session fixture from the shared seed,
and strengthen return-to-Weekend context coverage.
Co-authored-by: Cursor <cursoragent@cursor.com>
