Agent Skills: content-extract

Robust URL-to-Markdown extraction for OpenClaw workflows. Use when the user wants to "extract/summarize/convert a webpage to markdown" (especially WeChat mp.weixin.qq.com) and web_fetch/browser is blocked or messy. Uses a cheap probe via web_fetch first, then falls back to the official MinerU API (via the local mineru-extract skill) and returns a traceable result contract with source links.