feat(race-hub): trustworthy defaults and fan-facing analysis hierarchy (#75)

Make bare /race-hub resolve to a completed session and never open empty
post-session analysis for a future race.

- Backend: add `default_analysis_session` to the Weekend context. It never
  resolves to a future session (picks the richest completed session, ties
  toward the later one; 0 when everything is upcoming). Existing
  `default_session_key` and deep links are unchanged.
- Frontend default resolution prefers the most recently completed weekend
  (`pickAnalysisFocusMeeting`) and consumes `default_analysis_session`, falling
  back to the switcher when only upcoming sessions exist.
- New `sessionState` lib maps timing + coverage to user language
  (upcoming/live/preparing/partial/ready/cancelled); the session rail, active
  sub-bar, and WeekendSwitcher now label states instead of raw x/11 counts.
- Future sessions render a purpose-built PreSessionView (expected availability +
  countdown) instead of empty Winner/Podium/Pole/Strategy/Compare cards.
- Analysis navigation regrouped into Story / Analysis / Data & Context; every
  existing tab is preserved. Diagnostics (renamed from Data Status) is now a
  secondary action and the raw dataset strip is hidden behind an explicit
  toggle, so operational coverage no longer precedes fan content.
- Loading/error states offer Retry and a path back to Weekend.

Tests: Go query tests for future-exclusion; Vitest for default selection,
future pre-session, partial state, error/retry, grouped nav, and sessionState;
hermetic Playwright for bare/completed/future/return-to-Weekend; new
race-hub-future visual snapshots. Seed adds a far-future session inside the
Monaco meeting (kept in-meeting so Command Center focus is unaffected).

Note: `default_analysis_session` is an additive field on the existing
`/weekend` contract (no new endpoint), per the spec's "context contract" scope.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/components/OverviewView.tsx

@@ -148,7 +148,7 @@ export function OverviewView({ data }: Props) {
               ? 'Every Race Hub dataset is local for this session.'
               : `${coverage.total - coverage.available} dataset${
                   coverage.total - coverage.available === 1 ? '' : 's'
-                } not ingested yet — see Data Status tab.`}
+                } not ingested yet — see Diagnostics.`}
           </div>
         </section>
       </div>