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>

composer.json

@@ -1,7 +1,7 @@
 {
     "name": "magdev/wc-tier-package-prices",
     "description": "WooCommerce plugin for tier pricing and package prices with Twig templates",
-    "version": "1.3.1",
+    "version": "1.4.0",
     "type": "wordpress-plugin",
     "license": "GPL-2.0-or-later",
     "authors": [
@@ -12,14 +12,17 @@
     ],
     "repositories": [
         {
-            "type": "vcs",
-            "url": "https://src.bundespruefstelle.ch/magdev/wc-licensed-product-client.git"
+            "type": "path",
+            "url": "vendor/magdev/wc-licensed-product-client",
+            "options": {
+                "symlink": false
+            }
         }
     ],
     "require": {
         "php": ">=8.3",
         "twig/twig": "^3.0",
-        "magdev/wc-licensed-product-client": "dev-main"
+        "magdev/wc-licensed-product-client": "@dev"
     },
     "autoload": {
         "classmap": [