Client: mirror branded notification sound to customer app

The customer app now uses the same halobestie_notif.ogg as the mitra
app (shipped in the previous commit). Channel ID unified across both
apps so backend FCM stops branching per recipient.

- client_app: same channel bump (chat_messages → halobestie_chat_v1)
  + RawResourceAndroidNotificationSound binding, both at channel-
  create time and per-notification details. .ogg copied to
  client_app/android/app/src/main/res/raw/halobestie_notif.ogg
  (same 32 KB asset, identical file).
- Backend: drop the per-recipientType channel ID branch; everyone
  targets halobestie_chat_v1 now.

Verified on emulator-5554 (customer): dumpsys shows the channel
bound to android.resource://com.mybestie/raw/halobestie_notif.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/services/notification.service.js

@@ -21,14 +21,6 @@ export const sendPushNotification = async (recipientType, recipientId, { title,
 
   if (!user?.fcm_token) return false
 
-  // Mitra app ships a branded notification sound on its own channel
-  // (`halobestie_chat_v1`, declared in mitra_app/lib/core/notifications/
-  // notification_service.dart). Customer app keeps the legacy
-  // `chat_messages` channel until/unless we ship a customer sound too.
-  const androidChannelId = recipientType === UserType.MITRA
-    ? 'halobestie_chat_v1'
-    : 'chat_messages'
-
   try {
     await admin.messaging().send({
       token: user.fcm_token,
@@ -41,7 +33,10 @@ export const sendPushNotification = async (recipientType, recipientId, { title,
       },
       android: {
         priority: 'high',
-        notification: { channelId: androidChannelId },
+        // Both apps register the same channel ID with the branded
+        // notification sound (halobestie_notif.ogg in res/raw). See each
+        // app's lib/core/notifications/notification_service.dart.
+        notification: { channelId: 'halobestie_chat_v1' },
       },
       apns: {
         payload: {

client_app/lib/core/notifications/notification_service.dart

@@ -8,11 +8,17 @@ class NotificationService {
   static final _localNotifications = FlutterLocalNotificationsPlugin();
   static GoRouter? _router;
 
+  // Channel ID bumped (`chat_messages` → `halobestie_chat_v1`) when the
+  // branded notification sound was introduced. Android binds sound to a
+  // channel at create time on API 26+, so an existing channel can't pick
+  // up a new sound — a fresh ID is the only way. Backend FCM payloads
+  // target the same ID — see backend/src/services/notification.service.js.
   static const _channel = AndroidNotificationChannel(
-    'chat_messages',
-    'Chat Messages',
-    description: 'Notifications for incoming chat messages',
+    'halobestie_chat_v1',
+    'Chat HaloBestie',
+    description: 'Notifications for incoming chat messages and pairing requests',
     importance: Importance.high,
+    sound: RawResourceAndroidNotificationSound('halobestie_notif'),
   );
 
   static Future<void> initialize(GoRouter router) async {
@@ -60,6 +66,9 @@ class NotificationService {
           channelDescription: _channel.description,
           importance: Importance.high,
           priority: Priority.high,
+          // API 26+ ignores this in favor of the channel's sound; included
+          // for the API 24/25 path where channels don't exist yet.
+          sound: const RawResourceAndroidNotificationSound('halobestie_notif'),
         ),
         iOS: const DarwinNotificationDetails(
           presentAlert: true,