Initial date planner app (#2390)

Initial **experimental** date planner iOS sample.

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Style-guide-for-Flutter-repo.md
[CLA]: https://cla.developers.google.com/
[Discord]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Chat.md
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md

experimental/date_planner/lib/main.dart

@@ -0,0 +1,35 @@
+// Copyright 2024 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/cupertino.dart';
+import 'package:provider/provider.dart';
+
+import 'event_data.dart';
+import 'event_list.dart';
+
+void main() {
+  runApp(
+    ChangeNotifierProvider(
+      create: (context) => EventData(),
+      child: const DatePlannerApp(),
+    ),
+  );
+}
+
+CupertinoThemeData cupertinoLight = const CupertinoThemeData(
+  brightness: Brightness.light,
+  primaryColor: CupertinoColors.activeBlue,
+);
+
+class DatePlannerApp extends StatelessWidget {
+  const DatePlannerApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return CupertinoApp(
+      home: const EventList(),
+      theme: cupertinoLight,
+    );
+  }
+}