feat: initialize app with routing, query management, and UI framework

- Replace Vite boilerplate with React Router for page navigation
- Add React Query for server state and cache management
- Integrate shadcn/ui component library with Tailwind CSS v4
- Configure @/ path alias for clean module imports
- Set up Vite dev proxy to API backend
- Remove default App.css, App.tsx, and react.svg assets

src/router/index.tsx

@@ -0,0 +1,63 @@
+import { createBrowserRouter, Navigate } from "react-router-dom"
+import { ProtectedRoute, AdminRoute } from "./guards"
+
+// Placeholder components — real pages will replace these
+function LoginPage() {
+  return <div>Login</div>
+}
+function BooksPage() {
+  return <div>Books</div>
+}
+function MyBorrowsPage() {
+  return <div>My Borrows</div>
+}
+function AdminBooksPage() {
+  return <div>Admin / Books</div>
+}
+function AdminBorrowsPage() {
+  return <div>Admin / Borrows</div>
+}
+function AdminIndexPage() {
+  return <Navigate to="/admin/books" replace />
+}
+
+export const router = createBrowserRouter([
+  {
+    path: "/login",
+    element: <LoginPage />,
+  },
+  {
+    path: "/",
+    element: <Navigate to="/books" replace />,
+  },
+  {
+    path: "/books",
+    element: <BooksPage />,
+  },
+  {
+    element: <ProtectedRoute />,
+    children: [
+      {
+        path: "/my-borrows",
+        element: <MyBorrowsPage />,
+      },
+    ],
+  },
+  {
+    element: <AdminRoute />,
+    children: [
+      {
+        path: "/admin",
+        element: <AdminIndexPage />,
+      },
+      {
+        path: "/admin/books",
+        element: <AdminBooksPage />,
+      },
+      {
+        path: "/admin/borrows",
+        element: <AdminBorrowsPage />,
+      },
+    ],
+  },
+])