feat(notifications): register FCM token with backend post-login

Adds NotificationsRemoteDatasource in sf_shared that POSTs the current
Firebase Messaging token to /notifications/push, wired into the legacy
login flow right after getUserInfo so the device can receive targeted
push notifications.

Fire-and-forget with catchError so a failure never blocks login.

modules/legacy/modules/legacy_auth/lib/src/features/login/presentation/state/login_view_model.dart

@@ -19,6 +19,7 @@ class LegacyLoginViewModel extends Notifier<LegacyLoginViewState>
     with LoginFormValidation {
   late final LegacyLoginRepository _repository;
   late final GetUserInfoUseCase _getUserInfoUseCase;
+  late final NotificationsRemoteDatasource _notifications;
   late final SfTrackingRepository _tracking;
 
   late final TextEditingController emailController;
@@ -32,6 +33,7 @@ class LegacyLoginViewModel extends Notifier<LegacyLoginViewState>
   LegacyLoginViewState build() {
     _repository = ref.read(legacyLoginRepositoryProvider);
     _getUserInfoUseCase = ref.read(getUserInfoUseCaseProvider);
+    _notifications = ref.read(notificationsRemoteDatasourceProvider);
     _tracking = ref.read(sfTrackingProvider);
 
     emailController = TextEditingController();
@@ -224,6 +226,12 @@ class LegacyLoginViewModel extends Notifier<LegacyLoginViewState>
 
       if (!ref.mounted) return;
 
+      unawaited(
+        _notifications.registerCurrentPushToken().catchError((Object e) {
+          debugPrint('[FCM] failed to register push token post-login: $e');
+        }),
+      );
+
       final hasDevices = await _repository.hasDevices();
 
       if (!ref.mounted) return;