add React Router for extension import flow

- Install react-router-dom
- Create Router component with / and /import/:id routes
- Update main.tsx to use Router
- Enables URL-based navigation for extension imports

packages/web/package.json

···
     "lucide-react": "^0.544.0",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
+    "react-router-dom": "^7.11.0",
     "zustand": "^5.0.9"
   },
   "devDependencies": {

packages/web/src/Router.tsx

···
+import { BrowserRouter, Routes, Route } from 'react-router-dom';
+import App from './App';
+import ExtensionImport from './pages/ExtensionImport';
+
+/**
+ * Application Router
+ * Handles all routing for the application
+ */
+export default function Router() {
+  return (
+    <BrowserRouter>
+      <Routes>
+        {/* Main app route */}
+        <Route path="/" element={<App />} />
+
+        {/* Extension import route */}
+        <Route path="/import/:importId" element={<ExtensionImport />} />
+      </Routes>
+    </BrowserRouter>
+  );
+}

packages/web/src/main.tsx

···
 import React from "react";
 import ReactDOM from "react-dom/client";
-import App from "./App";
+import Router from "./Router";
 import "./index.css";
 
 ReactDOM.createRoot(document.getElementById("root")!).render(
   <React.StrictMode>
-    <App />
+    <Router />
   </React.StrictMode>,
 );