Fix listener serving DJ panel instead of listener page

- Block DJ-only files (index.html, script.js, style.css) on listener server
- Disable Flask built-in static handler on listener (static_folder=None)
  to prevent it from serving index.html before custom routes
- Add Cache-Control no-store headers to index route to prevent
  nginx/browser from caching stale index.html for listener URL

server.py

@@ -359,7 +359,11 @@ def setup_shared_routes(app, index_file='index.html'):
 
     @app.route('/')
     def index():
-        return send_from_directory('.', index_file)
+        response = send_from_directory('.', index_file)
+        response.headers['Cache-Control'] = 'no-store, no-cache, must-revalidate, max-age=0'
+        response.headers['Pragma'] = 'no-cache'
+        response.headers['Expires'] = '0'
+        return response
     
     @app.route('/upload', methods=['POST'])
     def upload_file():
@@ -661,19 +665,27 @@ def dj_audio(data):
             _feed_transcoder(bytes(data))
 
 # === LISTENER SERVER ===
-listener_app = Flask(__name__, static_folder='.', static_url_path='')
+# static_folder=None prevents Flask's built-in static handler from serving
+# DJ files (like index.html) at /<path> — all static files go through our
+# custom serve_static route which has security checks.
+listener_app = Flask(__name__, static_folder=None)
 listener_app.config['SECRET_KEY'] = CONFIG_SECRET + '_listener'
 listener_app.config['MAX_CONTENT_LENGTH'] = CONFIG_MAX_UPLOAD_MB * 1024 * 1024
 setup_shared_routes(listener_app, index_file='listener.html')
 
-# Block write/admin endpoints on the listener server
+# Block write/admin endpoints AND DJ-only files on the listener server
 @listener_app.before_request
 def _restrict_listener_routes():
-    """Prevent listeners from accessing DJ-only write endpoints."""
+    """Prevent listeners from accessing DJ-only endpoints and files."""
     blocked_paths = ('/update_settings', '/upload', '/save_keymaps', '/browse_directories')
     if request.path in blocked_paths:
         from flask import abort
         abort(403)
+    # Block DJ-only files — prevents serving the DJ panel even via direct URL
+    dj_only_files = ('/index.html', '/script.js', '/style.css')
+    if request.path in dj_only_files:
+        from flask import abort
+        abort(403)
 listener_socketio = SocketIO(
     listener_app, 
     cors_allowed_origins=CONFIG_CORS,