client: screens and app routing

Add all game screens: Login, Dashboard, Market (buy/sell), Inventory,
Missions, Travel (city selection), Leaderboard; wired via react-router
in App.tsx with protected routes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/src/App.tsx

@@ -0,0 +1,36 @@
+import { Navigate, Route, Routes } from 'react-router-dom';
+import { useAuth } from './auth/AuthContext';
+import { Layout } from './components/Layout';
+import { DashboardScreen } from './screens/DashboardScreen';
+import { InventoryScreen } from './screens/InventoryScreen';
+import { LeaderboardScreen } from './screens/LeaderboardScreen';
+import { LoginScreen } from './screens/LoginScreen';
+import { MarketScreen } from './screens/MarketScreen';
+import { MissionsScreen } from './screens/MissionsScreen';
+import { TravelScreen } from './screens/TravelScreen';
+
+export function App() {
+  const { token } = useAuth();
+
+  if (!token) {
+    return (
+      <Routes>
+        <Route path="*" element={<LoginScreen />} />
+      </Routes>
+    );
+  }
+
+  return (
+    <Routes>
+      <Route element={<Layout />}>
+        <Route path="/" element={<DashboardScreen />} />
+        <Route path="/market" element={<MarketScreen />} />
+        <Route path="/missions" element={<MissionsScreen />} />
+        <Route path="/inventory" element={<InventoryScreen />} />
+        <Route path="/travel" element={<TravelScreen />} />
+        <Route path="/leaderboard" element={<LeaderboardScreen />} />
+        <Route path="*" element={<Navigate to="/" replace />} />
+      </Route>
+    </Routes>
+  );
+}