Refactor license management and remove unused features

- Removed the JWT authentication setup and related access token handling.
- Deleted the test license activation functionality and associated routes.
- Removed the admin license management interface and related templates.
- Cleaned up the appointments page by removing test license options.
- Updated various templates to reflect changes in terminology from "license" to "instance".
- Removed the verify module and its associated functions for license key management.
- Deleted unused templates related to license management.
- Added a new empty JSON file for licenses backup.

Website/templates/inventarsystem.html

@@ -5,7 +5,7 @@
 {% block content %}
 <section class="page-hero">
     <h1>Inventarsystem für Schulen</h1>
-    <p>Alle wichtigen Funktionen für den Schulalltag in einer klaren Oberfläche: von Inventar über Lizenzen bis zur nachvollziehbaren Historie.</p>
+    <p>Alle wichtigen Funktionen für den Schulalltag in einer klaren Oberfläche: von Inventar bis zur nachvollziehbaren Historie.</p>
 </section>
 
 <section class="split">