Add a connectable AIGC canvas to DeepSeek Harness with dsh-plugin-aigc-canvas

# 翻译结果： The dsh-plugin-aigc-canvas, maintained by HuanLinOTO, provides provider-agnostic AIGC HTTP bridge, session-level canvas and ffmpeg post-processing for DeepSeek Harness. It first looks up the provider before sending requests (the API key is attached by the host), places files on the canvas and connects edges according to references. The default stub only synthesizes test media. Install via the catalog page: `dsh plugin add github:HuanLinOTO/dsh-plugin-aigc-canvas`. The plugin runs with the current DSH process permissions, please inspect the source code and license before installation.