Implement self-licensing (v0.3.0) and settings sub-tabs (v0.3.1)

v0.3.0 - Self-Licensing:
- Add PluginLicenseChecker singleton for license validation
- Integrate magdev/wc-licensed-product-client library
- Add license settings: server URL, key, optional secret
- Disable frontend features without valid license (except localhost)
- Add license status display with verify button in settings

v0.3.1 - Settings UI Improvements:
- Reorganize settings page with WooCommerce-style sub-tabs
- Split settings into: Plugin License, Default Settings, Notifications
- Use PHP 8 match expression for section-specific rendering

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

composer.json

@@ -10,9 +10,16 @@
             "homepage": "https://src.bundespruefstelle.ch/magdev"
         }
     ],
+    "repositories": [
+        {
+            "type": "path",
+            "url": "/home/magdev/workspaces/php/wc-licensed-product-client"
+        }
+    ],
     "require": {
         "php": ">=8.3.0",
-        "twig/twig": "^3.0"
+        "twig/twig": "^3.0",
+        "magdev/wc-licensed-product-client": "dev-main"
     },
     "autoload": {
         "psr-4": {