feat(frontend): add React dashboard with TypeScript

Add modern React frontend to replace Streamlit dashboard:
- Vite build system with TypeScript
- Tailwind CSS for styling
- Component structure in src/
- Production Dockerfile with nginx
- Development server on port 5173

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/App.tsx

@@ -0,0 +1,67 @@
+import { BrowserRouter, Routes, Route, Navigate } from 'react-router-dom';
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
+import { AuthProvider } from './context/AuthContext';
+import { Layout } from './components/Layout';
+import { ProtectedRoute } from './components/ProtectedRoute';
+import { Login } from './pages/Login';
+import { Register } from './pages/Register';
+import { Analysis } from './pages/Analysis';
+import { Batch } from './pages/Batch';
+import { AnalyticsPage } from './pages/Analytics';
+import { About } from './pages/About';
+import { AdminUsers } from './pages/AdminUsers';
+
+const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      staleTime: 1000 * 60 * 5, // 5 minutes
+      retry: 1,
+    },
+  },
+});
+
+function App() {
+  return (
+    <QueryClientProvider client={queryClient}>
+      <AuthProvider>
+        <BrowserRouter>
+          <Routes>
+            {/* Public routes */}
+            <Route path="/login" element={<Login />} />
+            <Route path="/register" element={<Register />} />
+
+            {/* Protected routes */}
+            <Route
+              element={
+                <ProtectedRoute>
+                  <Layout />
+                </ProtectedRoute>
+              }
+            >
+              <Route path="/analysis" element={<Analysis />} />
+              <Route path="/batch" element={<Batch />} />
+              <Route path="/analytics" element={<AnalyticsPage />} />
+              <Route path="/about" element={<About />} />
+
+              {/* Admin routes */}
+              <Route
+                path="/admin/users"
+                element={
+                  <ProtectedRoute requireAdmin>
+                    <AdminUsers />
+                  </ProtectedRoute>
+                }
+              />
+            </Route>
+
+            {/* Default redirect */}
+            <Route path="/" element={<Navigate to="/analysis" replace />} />
+            <Route path="*" element={<Navigate to="/analysis" replace />} />
+          </Routes>
+        </BrowserRouter>
+      </AuthProvider>
+    </QueryClientProvider>
+  );
+}
+
+export default App;