ui-next: page registration (#1159)

examples/plugins/ui-next-plugin/ui/index.tsx

@@ -0,0 +1,9 @@
+import type { PluginAPI } from '@hydrooj/ui-next';
+
+export function setup(api: PluginAPI) {
+    api.before('page:app', () => {
+        console.log('before app');
+        // throw new Error('test error boundary in before interceptor');
+        return <div>before app via @hydrooj/ui-next-plugin-sample</div>;
+    });
+}