feat(01-01): React + Vite + Tailwind v4 SPA scaffold con API client

- Vite react-ts project con base: '/postgenerator/' (Pitfall #9 risolto)
- Tailwind v4 via @tailwindcss/vite plugin + @import "tailwindcss" in index.css
- react-router-dom con BrowserRouter basename="/postgenerator"
- @tanstack/react-query con QueryClientProvider
- lucide-react installato per icone
- src/api/client.ts: API_BASE='/postgenerator/api', apiFetch<T> con error handling
- Dev proxy: /postgenerator/api -> http://localhost:8000 (strip /postgenerator)
- App.tsx: HomePage placeholder "Setup completo", struttura Routes pronta
- Build Vite: 253.90kB JS + 5.53kB CSS, nessun errore TypeScript

frontend/src/App.tsx

@@ -0,0 +1,37 @@
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { BrowserRouter, Route, Routes } from 'react-router-dom'
+
+const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      retry: 1,
+      staleTime: 30_000,
+    },
+  },
+})
+
+function HomePage() {
+  return (
+    <div className="min-h-screen bg-gray-950 text-gray-100 flex items-center justify-center">
+      <div className="text-center space-y-4">
+        <h1 className="text-4xl font-bold tracking-tight">PostGenerator</h1>
+        <p className="text-gray-400 text-lg">Setup completo — pronto per la business logic.</p>
+      </div>
+    </div>
+  )
+}
+
+function App() {
+  return (
+    <QueryClientProvider client={queryClient}>
+      {/* basename must match the nginx subpath and Vite base config */}
+      <BrowserRouter basename="/postgenerator">
+        <Routes>
+          <Route path="/" element={<HomePage />} />
+        </Routes>
+      </BrowserRouter>
+    </QueryClientProvider>
+  )
+}
+
+export default App