Fix CI/CD: Move submodule to lib/ directory like wp-fedistream

- Move submodule from vendor/magdev/ to lib/ to avoid Composer conflicts
- Use relative submodule URL (../wc-licensed-product-client.git)
- Pin submodule to v0.2.2 tag
- Update composer.json with ^0.2 version constraint
- Simplify .gitignore (no vendor exceptions needed)
- Update workflow to exclude lib/.git instead of vendor/.git

Based on working wp-fedistream implementation.

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

composer.json

@@ -13,20 +13,25 @@
     "repositories": [
         {
             "type": "path",
-            "url": "vendor/magdev/wc-licensed-product-client",
-            "options": {
-                "symlink": false
-            }
+            "url": "lib/wc-licensed-product-client"
         }
     ],
     "require": {
         "php": ">=8.3",
         "twig/twig": "^3.0",
-        "magdev/wc-licensed-product-client": "@dev"
+        "magdev/wc-licensed-product-client": "^0.2"
     },
     "autoload": {
         "classmap": [
             "includes/"
         ]
-    }
+    },
+    "config": {
+        "optimize-autoloader": true,
+        "platform": {
+            "php": "8.3.0"
+        }
+    },
+    "minimum-stability": "stable",
+    "prefer-stable": true
 }