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>

.vscode/launch.json

@@ -0,0 +1,43 @@
+{
+  "version": "0.2.0",
+  "configurations": [
+    // If the server pubspec configures multiple Flutter apps, add an attach
+    // configuration like this for each app and add every configuration name
+    // to the compound below. Use the VM-service info file pattern
+    // `${workspaceFolder}/halkyon_learn_server/.dart_tool/serverpod/flutter-vm-service-info-<appId>.json`,
+    // where `<appId>` is the app's key under `serverpod.flutter_apps` in the
+    // server pubspec.
+    {
+      // Attaches to the Flutter app `serverpod start` spawns. Don't
+      // launch a second instance here - it would race for the port.
+      "name": "halkyon_learn_flutter",
+      "type": "dart",
+      "request": "attach",
+      "vmServiceInfoFile": "${workspaceFolder}/halkyon_learn_server/.dart_tool/serverpod/flutter-vm-service-info-halkyon_learn.json",
+      "preLaunchTask": "serverpod_start",
+      "internalConsoleOptions": "neverOpen"
+    },
+    {
+      "name": "halkyon_learn_server",
+      "type": "dart",
+      "request": "attach",
+      "vmServiceInfoFile": "${workspaceFolder}/halkyon_learn_server/.dart_tool/serverpod/vm-service-info.json",
+      "preLaunchTask": "serverpod_start",
+      "internalConsoleOptions": "neverOpen"
+    }
+  ],
+  "compounds": [
+    {
+      "name": "halkyon_learn (full stack)",
+      "configurations": [
+        "halkyon_learn_server",
+        "halkyon_learn_flutter"
+      ],
+      // Stopping one session stops both; the orphan blocks re-attach.
+      "stopAll": true,
+      "presentation": {
+        "order": 1
+      }
+    }
+  ]
+}