fix(race-hub): consume canonical weekend context for #75 review

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>

tests/visual/helpers.ts

@@ -1,4 +1,5 @@
 import { expect, type Locator, type Page } from '@playwright/test'
+import { FUTURE_SESSION, mockFutureRaceHubSession } from '../fixtures/future-session'
 
 export const VIEWPORTS = {
   desktop: { width: 1280, height: 800 },
@@ -7,7 +8,7 @@ export const VIEWPORTS = {
 } as const
 
 export const FULL_SESSION = 9472
-export const FUTURE_SESSION = 9600
+export { FUTURE_SESSION }
 
 /** Wait for web fonts and layout to settle before screenshots. */
 export async function waitForScreenshotReady(page: Page): Promise<void> {
@@ -38,6 +39,7 @@ export async function gotoRaceHubFutureReady(
   page: Page,
   sessionKey = FUTURE_SESSION,
 ): Promise<void> {
+  await mockFutureRaceHubSession(page)
   await page.goto(`/race-hub?session_key=${sessionKey}`)
   await expect(page.getByTestId('race-hub')).toBeVisible()
   await expect(page.getByTestId('rh-presession')).toBeVisible()