feat(auth): wire AuthProvider + RequireAuth into app shell

src/main.tsx

@@ -2,6 +2,7 @@ import React from "react";
 import ReactDOM from "react-dom/client";
 import { BrowserRouter } from "react-router-dom";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { AuthProvider } from "@/auth/AuthProvider";
 import App from "./App";
 import "./index.css";
 
@@ -18,7 +19,13 @@ ReactDOM.createRoot(document.getElementById("root")!).render(
   <React.StrictMode>
     <QueryClientProvider client={queryClient}>
       <BrowserRouter>
-        <App />
+        {/* AuthProvider must sit inside BrowserRouter (so it can use
+            react-router hooks) but outside the route tree (so the
+            `/login` route still has access to auth state for the
+            auto-redirect when the operator is already signed in). */}
+        <AuthProvider>
+          <App />
+        </AuthProvider>
       </BrowserRouter>
     </QueryClientProvider>
   </React.StrictMode>