DeepSeek Harness Plugin deepseek-peak-valley-router: Auto-routing models based on peak-valley pricing

`deepseek-peak-valley-router` is an MIT-licensed plugin for DeepSeek Harness (DSH) designed to address the model selection challenge under DeepSeek V4 API peak-valley pricing. The plugin automatically identifies peak and idle periods; during peak times, it uses `deepseek-v4-flash` to control costs, and during idle times, it uses `deepseek-v4-pro` to prioritize performance, thereby eliminating the need for manual switching. Core features include: defaulting to the `Asia/Shanghai` timezone for period determination with support for custom timezones; always respecting the user's explicitly selected model without forcibly overriding it; only processing requests for specified DeepSeek V4 models while passing through others as-is; and logging all model switching operations in session events.