fix(frontend): wire passenger and staff pages to the API/hooks layer

[catomean]

Summary

• lib/api.ts + lib/hooks/useApi.ts implement "real API call, fall back to mock data" — exactly what CLAUDE.md documents as the frontend/backend integration — but no page ever called them. app/page.tsx, app/staff/page.tsx, and LostItemModal each hand-rolled their own setTimeout mock simulation instead, so the hooks layer was effectively dead code and the app never actually attempted a request against a configured backend.
• Wired all three to the existing hooks (useCurrentTrip, useTrips, useReportLostItem, useDriverNotificationsApi) so the documented fallback path actually runs, and removed the now-duplicate manual mock/timeout logic.
• Along the way this surfaced a real, previously-dormant bug in useDriverNotificationsApi: updateNotification's optimistic setLocalData bailed out whenever localData was still null (its initial value — nothing populated it before this hook had a caller), so the first found/not-found response silently no-op'd. Fixed by falling back to the fetched/mock data as the update base.
• Dropped the now-unreferenced mockDriverNotifications deprecated alias in mock-data.ts in favor of the canonical mockStaffNotifications it pointed to.

Test plan

• npx tsc --noEmit — clean
• npm run lint — 0 errors, same 3 pre-existing warnings (unchanged)
• npm test (frontend) — 32 pass
• npm test (reporting-service) — 27 pass
• npm run build — succeeds
• Manually drove both pages with a headless browser (dev server, no backend running so requests fail over to mock as intended): passenger trip list loads, report-lost flow (category → details → submit → success toast) completes end-to-end via useReportLostItem, staff notification list loads, and the found/not-found response buttons now correctly update the clicked card's status (previously broken before the hook fix, verified before/after).

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