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>

tests/visual/mvp-screens.spec.ts

@@ -3,6 +3,7 @@ import {
   gotoWeekendReady,
   gotoDataLibraryReady,
   gotoLiveEmptyReady,
+  gotoRaceHubFutureReady,
   gotoRaceHubReady,
   screenshotPage,
 } from './helpers'
@@ -18,6 +19,14 @@ test.describe('MVP visual regression', () => {
     await screenshotPage(page, 'race-hub')
   })
 
+  test('race-hub-future', async ({ page }) => {
+    await gotoRaceHubFutureReady(page)
+    // The countdown ticks every second — mask it so the snapshot stays stable.
+    await screenshotPage(page, 'race-hub-future', {
+      mask: [page.getByTestId('rh-presession-countdown')],
+    })
+  })
+
   test('data-library', async ({ page }) => {
     await gotoDataLibraryReady(page)
     await screenshotPage(page, 'data-library')