feat(todo): the server on halkyon_base

Todo's server includes halkyon_base (ADR 0014), configured for Todo:
its basics say it serves `todo`, sign-in mails name Halkyon Todo, the
source is this repository, minimumAppBuild 1. Authentication through
the module (anonymous, GitHub, email codes, server-side sessions) in
place of the scaffold's email-and-password provider; the module's
pruning scheduled once however often the server starts. The scaffold's
greeting, its Flutter web hosting, cloud storage and Docker files go;
session logs are never persisted. Todo was never deployed, so its
migrations start again with one initial migration. The root's lints
apply, with the four constructor rules off as on Learn's server.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/todo/halkyon_todo_server/test/integration/support/todo_fixtures.dart

@@ -0,0 +1,17 @@
+import 'package:halkyon_base_server/base.dart';
+import 'package:halkyon_todo_server/src/todo_base.dart';
+import 'package:serverpod_auth_idp_server/core.dart';
+
+import '../test_tools/serverpod_test_tools.dart';
+
+/// Sets the server up as it runs (lib/server.dart): halkyon_base as Todo
+/// configures it (ADR 0014), and authentication. On the pod [sessionBuilder]'s
+/// sessions run on, not on `Serverpod.instance`: that is the pod made last.
+void useTodoBase(TestSessionBuilder sessionBuilder) {
+  final pod = sessionBuilder.build().serverpod;
+  HalkyonBase.configure(pod, todoBase());
+  AuthServices.set(
+    tokenManagerBuilders: tokenManagerBuilders,
+    identityProviderBuilders: identityProviderBuilders(pod),
+  );
+}