use xdg_desktop_portal over flutter_local_notifications on linux

lib/controllers/portal.dart

@@ -0,0 +1,17 @@
+import "package:flutter_riverpod/flutter_riverpod.dart";
+import "package:xdg_desktop_portal/xdg_desktop_portal.dart";
+
+class PortalController extends AsyncNotifier<XdgDesktopPortalClient> {
+  @override
+  Future<XdgDesktopPortalClient> build() async {
+    final portal = XdgDesktopPortalClient();
+    await portal.registerApplication("nexus.federated.nexus");
+
+    return portal;
+  }
+
+  static final provider =
+      AsyncNotifierProvider<PortalController, XdgDesktopPortalClient>(
+        PortalController.new,
+      );
+}