Initial commit: Mathe-App Phase 1-3

- React+Vite Frontend mit Routing, eigenem fetch-Client (kein axios)
- Express Backend: Auth (JWT), Topics, Tasks, Leaderboard
- PostgreSQL Schema + Seed: 7 Kategorien, 21 Topics, ~25 Aufgaben
- Gamification: XP, Level (100×n^1.5), tägliche Streaks
- docker-compose auf Port 3100 für DS1621
- Alltagsaufgaben: Finanzen, Geometrie, Physik, Informatik, Verkehr, Shopping

frontend/src/App.jsx

@@ -0,0 +1,19 @@
+import { Routes, Route, Navigate } from 'react-router-dom'
+import Home from './pages/Home.jsx'
+import Login from './pages/Login.jsx'
+import Register from './pages/Register.jsx'
+import Dashboard from './pages/Dashboard.jsx'
+import TopicPage from './pages/TopicPage.jsx'
+
+export default function App() {
+  return (
+    <Routes>
+      <Route path="/" element={<Home />} />
+      <Route path="/login" element={<Login />} />
+      <Route path="/register" element={<Register />} />
+      <Route path="/dashboard" element={<Dashboard />} />
+      <Route path="/topic/:slug" element={<TopicPage />} />
+      <Route path="*" element={<Navigate to="/" replace />} />
+    </Routes>
+  )
+}