chore: scaffold the Serverpod 4 build

Deviations from a stock `serverpod create`:
- Dropped Flutter web support, for two reasons:
  - Appflowy editor had issues in the past, potentially related to the
    Flutter-Web IME bridge. Upstream has also open bugs in relation to
that:
    - AppFlowy-IO/appflowy-editor#1029 [Bug][Web] Unwanted space on click
       and overall space bugs (open)
    - AppFlowy-IO/appflowy-editor#782 [Bug] Editor auto-scrolling when
       pressing space too quickly if placed inside a scrollable (open)
  - Offline-first is a required feature. serverpod_offline_sync's SQLite
    support in browsers, maybe via sqlite3.wasm + OPFS, is not
documented.
- SDK constraints raised to ^3.13.0, instead of ^3.12.2, so enjoy the
  newest language features.
- Pinned to Flutter 3.47.4 via FVM.

Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/lib/driver.dart

@@ -0,0 +1,15 @@
+// This file is never meant to be used on real apps, just for development.
+// ignore: depend_on_referenced_packages
+import 'package:flutter_driver/driver_extension.dart';
+
+import 'main.dart' as app;
+
+void main() {
+  enableFlutterDriverExtension(
+    // Text entry emulation is disabled by default to allow manual usage of the
+    // app, but will be required for agents to type through the app. Set this
+    // parameter to true to switch from manual to automated usage.
+    enableTextEntryEmulation: false,
+  );
+  app.main();
+}