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>

README.md

@@ -1,2 +1,23 @@
 # AeonShopwareTools
 
+Scripting and developer tooling for Shopware 6.6 and 6.7.
+
+## Installation
+
+```bash
+composer require arthurerlich/aeon-shopware-tools
+bin/console plugin:refresh
+bin/console plugin:install --activate AeonShopwareTools
+```
+
+Or drop the release zip into `custom/plugins/` and install it from the admin.
+
+## Compatibility
+
+| Shopware | PHP    |
+|----------|--------|
+| 6.6, 6.7 | ^8.2   |
+
+## License
+
+MIT, see [LICENSE](LICENSE). Changes are listed in [CHANGELOG.md](CHANGELOG.md).