Add championship hub with derived stats and progression views

New /api/v1/championship/hub endpoint aggregates official standings with
wins, podiums, poles, recent form, teammate head-to-head, and per-round
cumulative points. ChampionshipPage renders drivers, constructors, and
progression views.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/components/Nav.tsx

@@ -16,6 +16,9 @@ export function Nav() {
         <Link to="/race-hub" search={{}} activeProps={{ className: 'active' }}>
           Race Hub
         </Link>
+        <Link to="/championship" activeProps={{ className: 'active' }}>
+          Championship
+        </Link>
         <Link to="/briefing" activeProps={{ className: 'active' }}>
           Briefing
         </Link>