dsh-token-usage-xc: DSH Token Usage Statistics Plugin

`dsh-token-usage-xc` is a DeepSeek Harness (DSH) plugin developed by xchannel1987, designed to provide visual token usage statistics and cache efficiency analysis. The plugin displays today’s token usage (including input, output, and cache reads/writes) on the settings page and automatically calculates the cache hit rate. It supports 7-day trend charts, session top-bar badge display, and persistent data storage. Additionally, the plugin provides an RPC interface for integration. The installation command is `dsh plugin --profile web add dsh-token-usage-xc`, and it is compatible with DSH 0.1.7-rc.1 and later versions.