fix push notification delivery on android

frontend/index.js

@@ -0,0 +1,27 @@
+// Custom entry point. The FCM background handler must be registered in the very
+// first module that loads — before the router/app mounts — so it reliably fires
+// when the app is backgrounded or fully quit. Registering it here (rather than in
+// app/_layout.tsx) is what react-native-firebase requires for the killed state.
+import messaging from '@react-native-firebase/messaging';
+import notifee, { AndroidImportance } from '@notifee/react-native';
+
+messaging().setBackgroundMessageHandler(async (remoteMessage) => {
+    const title = remoteMessage.data?.title;
+    const body = remoteMessage.data?.body;
+    if (!title && !body) return;
+
+    const channelId = await notifee.createChannel({
+        id: 'default',
+        name: 'General',
+        importance: AndroidImportance.HIGH,
+    });
+
+    await notifee.displayNotification({
+        title,
+        body,
+        android: { channelId, pressAction: { id: 'default' } },
+    });
+});
+
+// Hand off to expo-router, which mounts app/_layout.tsx and the routes.
+import 'expo-router/entry';