dsh-writing-studio: DeepSeek Harness Long-Form Writing Plugin

The `dsh-writing-studio` plugin for DeepSeek Harness is designed to address context limits, style consistency, and state-loss issues in long-form document writing. It serves as a state machine and persistence layer, providing end-to-end tools for project setup, outlining, section-by-section drafting, proofreading, and final assembly. It supports eight common templates and style control. The plugin persists data using local JSON files, has zero runtime dependencies, and supports both automated workflow and manual control modes, helping developers complete long-form writing more efficiently.