feat: hide logout button when admin is not logged in

- Add conditional rendering for "Abmelden" button based on isAdminLoggedIn state
- Button only appears when localStorage contains "isAdminLoggedIn": "true"
- Improves UI cleanliness by hiding unnecessary logout option for regular users
- Maintains existing admin warning banner and logout functionality when needed

package.json

@@ -1,6 +1,6 @@
 {
   "name": "cpl-v4",
-  "version": "1.6.669",
+  "version": "1.6.670",
   "private": true,
   "scripts": {
     "dev": "next dev",