chore: scaffold Laravel 13 core app

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BCrwHHnGCB5XH968Nxokqw

core/tests/TestCase.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace Tests;
+
+use Illuminate\Foundation\Testing\TestCase as BaseTestCase;
+
+abstract class TestCase extends BaseTestCase
+{
+    //
+}