dsh-tool-describe-image: Add image understanding capability to DSH

`sala003/dsh-tool-describe-image` is an MIT-licensed plugin within the DSH ecosystem designed to equip text models with image processing capabilities. By connecting to any OpenAI-compatible vision endpoint (such as Bailian, Zhipu AI, etc.), it converts images into text descriptions or structured HTML for use with DeepSeek. Core features include a Web interface for "paste and recognize," tool invocation via path to describe images, querying DeepSeek account balance, and providing a customizable entry point for a "Whale Girl" desk pet. The plugin supports zero-configuration startup, allowing API keys to be configured later via environment variables or the settings panel. Installation requires DSH 0.1.0-rc.6+, installed globally via npm and enabled. It supports PNG, JPG, WebP, and GIF formats, with a single-image limit of 8Mi.