fix: use Path.read_text() instead of open() in browser_tool

tools/browser_tool.py

@@ -1523,7 +1523,7 @@ def cleanup_browser(task_id: Optional[str] = None) -> None:
                 pid_file = os.path.join(socket_dir, f"{session_name}.pid")
                 if os.path.isfile(pid_file):
                     try:
-                        daemon_pid = int(open(pid_file).read().strip())
+                        daemon_pid = int(Path(pid_file).read_text().strip())
                         os.kill(daemon_pid, signal.SIGTERM)
                         logger.debug("Killed daemon pid %s for %s", daemon_pid, session_name)
                     except (ProcessLookupError, ValueError, PermissionError, OSError):