dsh-client-ui-peak-valley: DSH Web Client Peak/Valley Price Status Display Plugin

The DeepSeek Harness plugin `dsh-client-ui-peak-valley` displays the DeepSeek API pricing status in real time at the UI layer. It automatically checks Beijing time every 30 seconds and uses colors (green/orange) to distinguish off-peak from peak pricing, helping developers optimize costs. Installation requires the `dshpm` command and a process restart. It only supports sessions whose model ID contains `deepseek`, and is compatible with light and dark themes.