Add wc-licensed-product-client as git submodule

- Bundle magdev/wc-licensed-product-client as git submodule
- Update composer.json to use path repository instead of VCS
- Update .gitignore to allow submodule in vendor directory
- Update CI workflow to checkout submodules recursively
- Remove private repository authentication step (no longer needed)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -3,7 +3,10 @@
 Thumbs.db
 
 # Composer
-/vendor/
+/vendor/*
+!/vendor/magdev/
+/vendor/magdev/*
+!/vendor/magdev/wc-licensed-product-client/
 composer.lock
 
 # Twig cache