dsh-llmasking: DeepSeek Harness Transport Layer Data Masking Plugin

The DeepSeek Harness plugin `dsh-llmasking` is designed to address the risk of sensitive information leakage. It intercepts model calls and masks data before transmission, ensuring that the model receives only placeholders while local logs and the UI continue to display real values. The plugin supports detection of multiple types of sensitive data, such as email addresses, bank card numbers, IP addresses, and identity card numbers, and features streaming processing, zero-overhead pass-through, and fail-safe mechanisms. No configuration changes are required under the default settings, and the `/llmasking` command can be used to monitor its status or verify its effectiveness.