dsh-remote-tunnel: Connecting Remote dsh Web to a Local SSH Tunnel

`dsh-remote-tunnel` is a Remote Host Tunnel Manager plugin for DSH, designed to simplify the complex workflow of running `dsh web` on remote Linux servers. By encapsulating port allocation, registry management, systemd supervision, and SSH tunnel maintenance, this plugin allows users to maintain only a single local SSH tunnel, thereby avoiding manual handling of details such as port conflicts, disconnection and reconnection, and system service configuration. Core features include: automatically allocating an independent remote port for each user and recording it to the registry; utilizing user-level or system-level systemd to supervise remote services; employing a resilient SSH tunneling mechanism that supports automatic reconnection upon network interruptions and heartbeat keep-alive; and intelligently handling local end...