chore: Halkyon Todo's scaffold joins the repository in apps/todo

Its server, client and app as `serverpod create` made them, with the
switch to server-side sessions that was waiting uncommitted, as files:
its one commit holds the scaffold alone.

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_client/doc/endpoint.md

@@ -0,0 +1,15 @@
+# Callable endpoints
+
+Each class contains callable methods that will call a method on the server side. These are normally defined in the `endpoint` directory in your server project. This client sends requests to these endpoints and returns the result.
+
+Example usage:
+
+```dart
+// How to use GreetingEndpoint.
+client.greeting.hello("world!");
+
+// Generic format.
+client.<endpoint>.<method>(...);
+```
+
+Please see the full official documentation [here](https://docs.serverpod.dev)