dsh-keepalive: Add an optional watchdog for the DSH Web process

dsh-keepalive is an MIT-licensed plugin maintained by xiaohj233, designed specifically for the DeepSeek Harness (DSH) Web process. Its core functionality is to run a detached watchdog to monitor the status of the DSH Web process and automatically restart it with the same parameters after the process exits. The plugin supports manual restarts via API or the UI, and provides an optional repair agent that performs repairs, validation, and rollback based on snapshots within a controlled workspace when repeated startup failures occur. Usage requires specific Node.js and pnpm versions and can be installed via a command. After installation, restart the Web profile and explicitly enable `enable` in the configuration.