build-dsh-plugin: DSH Plugin Development Workflow

`build-dsh-plugin` is an Agent Skill developed by AI-Scarlett, designed to simplify DeepSeek Harness (DSH) plugin development through standardized workflows. It converts a Brief into an engineering plan, with built-in host compatibility checks, R0-R3 risk assessment, and store-compatible structure generation, ensuring that plugins comply with DSH Store specifications from the development stage. Once installed, the tool can produce analysis reports, source code, and audit workflows based on a Brief, support isolated testing, and generate store structures that meet listing requirements.