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/tasks.json

@@ -0,0 +1,48 @@
+{
+  "version": "2.0.0",
+  "tasks": [
+    {
+      "label": "serverpod_start",
+      "type": "shell",
+      "command": "serverpod",
+      "args": ["start"],
+      "options": {
+        "cwd": "${workspaceFolder}/halkyon_learn_server",
+        "env": {
+          "SERVERPOD_PASSWORD_database": "zLZiS0hYW86MNDWF3fTB9iYudoEQ4rZG",
+          // Marks a `serverpod start` launched from the IDE, which is the
+          // only kind that honors the Flutter device picked in VS Code. A run
+          // started from a plain terminal carries no marker, so a device file
+          // left behind by a session that was killed cannot retarget it.
+          "SERVERPOD_LAUNCHED_FROM_IDE": "true"
+        }
+      },
+      "isBackground": true,
+      "presentation": {
+        "reveal": "always",
+        "panel": "dedicated"
+      },
+      // The TUI captures stdout, so we can't string-match for "ready". The
+      // attach config polls vm-service-info.json for the actual readiness
+      // signal; this matcher exists only to satisfy VS Code's requirement
+      // that background tasks declare one. The pattern intentionally never
+      // matches; begin/end patterns mark the task active+ready immediately.
+      "problemMatcher": {
+        "owner": "serverpod",
+        "pattern": [
+          {
+            "regexp": "^(SERVERPOD_NEVER_MATCH):(\\d+):(.+)$",
+            "file": 1,
+            "line": 2,
+            "message": 3
+          }
+        ],
+        "background": {
+          "activeOnStart": true,
+          "beginsPattern": ".",
+          "endsPattern": "."
+        }
+      }
+    }
+  ]
+}