move NotificationsPage into sidebar via NavigationBar

lib/widgets/invites_list.dart

@@ -0,0 +1,22 @@
+import "package:flutter_riverpod/flutter_riverpod.dart";
+import "package:material_ui/material_ui.dart";
+import "package:nexus/models/nav_page.dart";
+
+class const InvitesList({super.key})
+    extends StatelessWidget
+    implements NavPage {
+  @override
+  String get title => "Invites";
+
+  @override
+  IconData get icon => Icons.inbox;
+
+  // TODO: Show notification badge here
+  @override
+  Future<int>? badgeBuilder(WidgetRef ref) => null;
+
+  @override
+  Widget build(BuildContext context) {
+    return const Placeholder();
+  }
+}