增加Scheme无法找到的警告页面。

src/App.tsx

@@ -4,6 +4,7 @@ import { Home } from './pages/Home';
 import { MainLayout } from './pages/MainLayout';
 import { NewScheme } from './pages/NewScheme';
 import { SchemeDetail } from './pages/SchemeDetail';
+import { SchemeNotFound } from './pages/SchemeNotFound';
 import { Schemes } from './pages/Schemes';
 
 const routes = createBrowserRouter([
@@ -17,6 +18,7 @@ const routes = createBrowserRouter([
         element: <Schemes />,
         children: [
           { path: 'new', element: <NewScheme /> },
+          { path: 'not-found', element: <SchemeNotFound /> },
           { path: ':id', element: <SchemeDetail /> },
         ],
       },

src/pages/SchemeNotFound.module.css

@@ -0,0 +1,6 @@
+@layer pages {
+  .unexists {
+    font-size: var(--font-size-xl);
+    color: var(--color-danger);
+  }
+}

src/pages/SchemeNotFound.tsx

@@ -0,0 +1,11 @@
+import styles from './SchemeNotFound.module.css';
+
+export function SchemeNotFound() {
+  return (
+    <div className="center">
+      <div className={styles.unexists}>
+        Request scheme is <strong>NOT</strong> exists.
+      </div>
+    </div>
+  );
+}