Fix delete JSON error: API routes return 401 JSON instead of HTML redirect, robust fetch error handling

app.py

@@ -438,6 +438,9 @@ def login_required(f):
     @wraps(f)
     def decorated_function(*args, **kwargs):
         if not session.get('authenticated'):
+            # API-Routen (/api/...) geben JSON zurück statt HTML-Redirect
+            if request.path.startswith('/api/'):
+                return jsonify({'success': False, 'error': 'not_authenticated'}), 401
             return redirect(url_for('login'))
         return f(*args, **kwargs)
     return decorated_function