feat: Add CalendarSelector component and install new dependencies.

client/src/App.jsx

@@ -0,0 +1,36 @@
+import { BrowserRouter, Routes, Route, Outlet } from 'react-router-dom';
+import CreateEvent from './components/CreateEvent';
+import EventPoll from './components/EventPoll';
+import AnalyticsDashboard from './components/AnalyticsDashboard';
+
+function Layout() {
+  return (
+    <div className="min-h-screen bg-slate-50 flex flex-col items-center p-4 sm:p-6 font-sans text-slate-900">
+      <header className="w-full max-w-2xl flex justify-between items-center py-6 mb-8">
+        <div className="text-xl font-bold tracking-tight text-slate-900 flex items-center gap-2">
+          <span className="w-8 h-8 rounded-lg bg-primary text-white flex items-center justify-center font-serif italic text-lg shadow-stripe">e</span>
+          eventy
+        </div>
+      </header>
+      <main className="w-full max-w-2xl relative z-10">
+        <Outlet />
+      </main>
+    </div>
+  );
+}
+
+function App() {
+  return (
+    <BrowserRouter>
+      <Routes>
+        <Route element={<Layout />}>
+          <Route path="/" element={<CreateEvent />} />
+          <Route path="/event/:id" element={<EventPoll />} />
+          <Route path="/event/:id/analytics" element={<AnalyticsDashboard />} />
+        </Route>
+      </Routes>
+    </BrowserRouter>
+  );
+}
+
+export default App;