dsh-session-stats-panel: DeepSeek Harness Real-Time Session Statistics and Billing Dashboard

`dsh-session-stats-panel` is a DeepSeek Harness client plugin designed to address the lack of real-time monitoring capabilities for developers. It is docked non-intrusively on the right side of the page, providing core metrics such as token cache hit rate, estimated official peak/off-peak billing, account balance, runtime, and cumulative tokens. The plugin uses a server-side credential isolation design to ensure that API keys are processed only on the server, enabling secure real-time monitoring of session data and costs.