dsh-session-showcase: Organize DSH sessions into local GIF demos for README

dsh-session-showcase is a standalone MIT-licensed community tool designed to organize DeepSeek Harness (DSH) session exports into demo materials suitable for GitHub READMEs. It supports reading official ZIP archives, raw session.jsonl files, or Zstandard logs, and generates WebP/GIF animations, posters, social preview images, README snippets, and machine-readable manifests locally. This tool runs entirely locally with zero AI model calls, requiring no FFmpeg or API keys, and only demands Node.js 22.19+. When used as a DSH plugin, it registers the `dsh_showcase` tool; it can also be built as a standalone CLI from source.