Add WebSocket authentication via api_key

- When --api_key is set, WebSocket connections require auth too
- Supports Authorization: Bearer <key> header or ?token=<key> query param
- Unauthenticated connections receive HTTP 401 before upgrade
- Uses websockets process_request callback (no resource allocation before auth)
- Added 5 unit tests for WebSocket auth handler

run_server.py

@@ -100,8 +100,8 @@ if __name__ == "__main__":
         '--api_key',
         type=str,
         default=None,
-        help='Optional API key for authenticating REST API requests. '
-             'Clients must send "Authorization: Bearer <key>" header.'
+        help='Optional API key for authenticating REST API and WebSocket connections. '
+             'Clients must send "Authorization: Bearer <key>" header or "?token=<key>" query parameter.'
     )
     parser.add_argument(
         '--rate_limit_rpm',