feat: Add license management and tabbed settings (v0.3.0)

- Implement license management using magdev/wc-licensed-product-client
- Reorganize settings page into License, Default Settings, Integrations tabs
- Add license validation and activation via AJAX
- Frontend features require valid license (admin works always)
- Update translations with German (de_CH) for license strings

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

composer.json

@@ -14,8 +14,15 @@
     "support": {
         "issues": "https://src.bundespruefstelle.ch/magdev/wp-fedistream/issues"
     },
+    "repositories": [
+        {
+            "type": "vcs",
+            "url": "https://src.bundespruefstelle.ch/magdev/wc-licensed-product-client.git"
+        }
+    ],
     "require": {
         "php": ">=8.3",
+        "magdev/wc-licensed-product-client": "^0.1",
         "twig/twig": "^3.0"
     },
     "require-dev": {