dsh-usage-board: DeepSeek Harness Usage and Cost Visualization Dashboard Plugin

`dsh-usage-board` is a client plugin for DeepSeek Harness (DSH) designed to address token consumption, cost accounting, and performance diagnostics in agent orchestration. It provides real-time monitoring, historical traceability, DAG relationship analysis, and cost insights, supporting cold-start trace-back, a dual-layer read model, and UI mounting. Built on Node.js native SQLite, the plugin adopts a zero-dependency architecture and CQRS design, using DSH session files as the source of truth with all data stored locally. Users can configure an API Key to view official balances and use the provided TypeScript interfaces for secondary development.