fix(#73): consume canonical Weekend Context contract and repair navigation

Address the independent review blockers on PR #80 after rebasing onto the
authoritative #72 Weekend Context API.

- Replace the invented frontend WeekendContext with the exact backend contract
  (temporal_state, previous/focus/next meetings, previous_completed/active/next/
  default_analysis sessions with availability). Every valid canonical payload now
  maps to a designed state via a total resolveViewState; a well-formed response
  can never fall through to the limited-data placeholder.
- Make the canonical read the single source of truth: useWeekendContext no longer
  fans out to season/meetings/per-weekend/OpenF1/live queries. Only supplementary
  championship + news reads run, and only once the canonical context resolves.
- Fix the Prepare/analysis flow: /preview is a stable alias that renders the
  preparation surface (PreSessionView) instead of redirecting back to the same
  between-races screen.
- One primary navigation system per breakpoint: the mobile top-bar links are
  hidden so the bottom bar is the sole primary nav, and Admin is moved out of
  every Primary landmark into an operator-utilities toolbar.
- Add Vitest coverage for the contract mapping, every temporal state, loading/
  error/limited surfaces, the no-fanout guarantee, the /preview CTA, and the nav
  hierarchy; add hermetic Playwright journeys (seeded + injected canonical
  payloads), 390/768/1440 overflow checks, and Weekend visual snapshots. Retire
  the stale Command Center specs/snapshots.

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

tests/visual/helpers.ts

@@ -14,16 +14,13 @@ export async function waitForScreenshotReady(page: Page): Promise<void> {
   await page.waitForTimeout(150)
 }
 
-export async function gotoCommandCenterReady(page: Page): Promise<void> {
+export async function gotoWeekendReady(page: Page): Promise<void> {
   await page.goto('/')
-  await expect(page.getByTestId('command-center')).toBeVisible()
-  await expect(page.getByTestId('cc-focus')).toBeVisible()
-  await expect(page.getByTestId('cc-session-9472')).toBeVisible()
-  // The e2e stack runs with an unreachable OpenF1 base URL, so wait for the
-  // season-calendar query to settle on its local fallback before screenshotting.
-  await expect(
-    page.getByText('Using local meetings because the full calendar could not load.'),
-  ).toBeVisible()
+  await expect(page.getByTestId('weekend-page')).toBeVisible()
+  // The seeded hermetic DB (Monaco 2025, completed) resolves to season_complete,
+  // rendered by the between-races surface.
+  await expect(page.getByTestId('weekend-between-races')).toBeVisible()
+  await expect(page.getByTestId('wk-last-event')).toBeVisible()
   await waitForScreenshotReady(page)
 }