dsh-ppt: DSH Presentation Plugin

The DSH plugin `dsh-ppt` is designed to address the pain points of manually creating PPT presentations. It supports generating an HTML web page and a PPTX file with one click from plain text or Markdown. Implemented in pure Node.js with zero dependencies, the plugin includes core features such as seven slide types, five themes, and speaker notes. It is compatible with both DSH skill registration and bare CLI build modes, generating a “three-piece set” of files to support both online presentation and offline editing. It currently supports 16:9 PPTX editing and requires Node.js 22.19.0 or later. Charts and images are not yet supported.