feat: plugin skeleton for Shopware 6.6 and 6.7 with CI and release pipeline

- composer.json (MIT, shopware/core ~6.6.0 || ~6.7.0, PHP ^8.2), plugin class, placeholder icon
- PR checks and release workflow taken over from AeonDumpManager; phpunit runs as a 6.6/6.7 matrix
- CHANGELOG, LICENSE, README, CLAUDE.md, smoke test

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/TestBootstrap.php

@@ -0,0 +1,12 @@
+<?php declare(strict_types=1);
+
+use Shopware\Core\TestBootstrapper;
+
+$loader = (new TestBootstrapper())
+    ->addCallingPlugin()
+    ->addActivePlugins('AeonShopwareTools')
+    ->setForceInstallPlugins(true)
+    ->bootstrap()
+    ->getClassLoader();
+
+$loader->addPsr4('AeonShopwareTools\\Tests\\', __DIR__);