dsh-tool-ssh: SSH/SFTP Tool Plugin for DeepSeek Harness

`dsh-tool-ssh` is an open-source plugin developed for DeepSeek Harness (DSH), designed to address the lack of native SSH/SFTP capabilities in web environments and provide a remote access experience similar to MobaXterm. The plugin supports session management, command execution, and file transfer, and ensures persistent connection reuse so that sessions remain active when switching views. After installation, users can manage remote Linux hosts through CLI tools such as `ssh_exec` and `ssh_upload` using saved connection configurations, with support for file read/write operations and SFTP transfers, along with an optimized web GUI interface. When using the plugin, note that keys and passwords are stored in plaintext; users should ensure local security and confirm that remote host ports are accessible.