M1: implement operational core

Demo auth, seed import/reset, dashboard, vehicle/booking list+detail, audit trail. Backend: 19 tests passing, ruff clean. Frontend: React Router shell, typed API client, responsive pages. Verified end-to-end via curl and browser.

frontend/src/main.tsx

@@ -1,10 +1,13 @@
 import React from "react";
 import ReactDOM from "react-dom/client";
+import { BrowserRouter } from "react-router-dom";
 import { App } from "./App";
 import "./styles.css";
 
 ReactDOM.createRoot(document.getElementById("root")!).render(
   <React.StrictMode>
-    <App />
+    <BrowserRouter>
+      <App />
+    </BrowserRouter>
   </React.StrictMode>,
 );