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_server/config/test.yaml

@@ -0,0 +1,57 @@
+# This is the configuration file for your test environment.
+# All ports are set to zero in this file which makes the server find the next available port.
+# This is needed to enable running tests concurrently. To set up your server, you will
+# need to add the name of the database you are connecting to and the user name.
+# The password for the database is stored in the config/passwords.yaml.
+#
+# When running your server locally, the server ports are the same as the public
+# facing ports.
+
+# Configuration for the main API test server.
+apiServer:
+  port: 0
+  publicHost: localhost
+  publicPort: 0
+  publicScheme: http
+
+# Configuration for the Insights test server.
+insightsServer:
+  port: 0
+  publicHost: localhost
+  publicPort: 0
+  publicScheme: http
+
+# Configuration for the web test server.
+webServer:
+  port: 0
+  publicHost: localhost
+  publicPort: 0
+  publicScheme: http
+
+# This is the database setup for your test server.
+database:
+  host: localhost
+  port: 9090
+  name: halkyon_learn_test
+  user: postgres
+  dataPath: .serverpod/test/pgdata
+  #maxConnectionCount: 10 # Defaults to 10, a negative or null value removes the limit
+
+# This is the setup for your Redis test instance.
+redis:
+  enabled: false
+  host: localhost
+  port: 9091
+  #user: # defaults to empty
+  #requireSsl: true # defaults to false
+
+sessionLogs:
+  persistentEnabled: true
+  consoleEnabled: true
+# consoleLogFormat: json # Defaults to "json", options are "text" or "json"
+
+# futureCallExecutionEnabled: true # Defaults to true
+
+#futureCall:
+#  concurrencyLimit: 1 # Defaults to 1, a negative or null value removes the limit
+#  scanInterval: 5000 # Unit in milliseconds, defaults to 5000