Onboarding steps 1 and 2 (mock 1h) with first-run redirect (#91)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>

web/src/onboarding/OnboardingGate.tsx

@@ -0,0 +1,52 @@
+import { useEffect } from 'react'
+import { Navigate, Outlet, useLocation } from 'react-router'
+import { useApi } from '../api/index.ts'
+import { LoadingScreen } from '../AuthBootstrap.tsx'
+import { useHouseholdSettings } from '../settings/api.ts'
+import { ErrorBanner } from '../ui/ErrorBanner.tsx'
+import styles from '../pages/FullScreen.module.css'
+
+export const ONBOARDING_PATH = '/onboarding'
+
+function inOnboarding(pathname: string): boolean {
+  return pathname === ONBOARDING_PATH || pathname.startsWith(`${ONBOARDING_PATH}/`)
+}
+
+// OnboardingGate reads the household settings before any page: while
+// onboarding_completed_at is null, every route outside /onboarding
+// redirects there.
+//
+// The service worker never caches the settings, so offline on the saved
+// pages (see AuthBootstrap) they cannot be read: the saved pages open as they
+// are, since onboarding needs the server anyway, and the settings are read
+// again when the browser is back online.
+export function OnboardingGate() {
+  const api = useApi()
+  const { pathname } = useLocation()
+  const settings = useHouseholdSettings()
+  const offline = settings.isError && settings.error instanceof TypeError && api.session.verified()
+  const { refetch } = settings
+
+  useEffect(() => {
+    if (!offline) return
+    return api.network.subscribe(() => {
+      if (!api.network.offline()) void refetch()
+    })
+  }, [offline, api, refetch])
+
+  if (settings.data !== undefined) {
+    if (settings.data.onboarding_completed_at === null && !inOnboarding(pathname)) {
+      return <Navigate to={ONBOARDING_PATH} replace />
+    }
+    return <Outlet />
+  }
+  if (offline) return <Outlet />
+  if (settings.isError) {
+    return (
+      <main className={styles.screen}>
+        <ErrorBanner onRetry={() => void refetch()}>MealQuest could not load: {settings.error.message}</ErrorBanner>
+      </main>
+    )
+  }
+  return <LoadingScreen />
+}