dsh-period-report: DeepSeek Harness Periodic Work Report Plugin

`dsh-period-report` is a DeepSeek Harness plugin designed to automatically generate periodic work reports using AI. It supports custom time ranges, uses AI to generate complete reports that include statistics and natural language summaries, and provides system notification reminders. It allows users to configure scheduled tasks, manage session data, and track token consumption and tool invocations, helping developers automate and standardize the reporting process.