Extracts the visual theme (colors, typography, radius, spacing, shadows) of a public website provided by the user and produces a shadcn/ui + Tailwind CSS v4 compatible token block, ready to paste into the project's `globals.css` (or `app.css`) inside `@theme` and `.dark`. Uses the `agent-browser` CLI to drive a real Chromium instance. Use when the user asks to "extract the theme of <url>", "reverse-engineer the design tokens of <site>", "copy the look of <site> into shadcn", "build a tailwind v4 theme from <url>", or mentions extract-theme / theme extraction / design tokens from a URL.
