Local dev server screenshot tool for visual QA

Use case

I was building a React component via Claude Code remotely (phone, SSH). The component built and compiled clean, but I couldn't visually verify the render — I wasn't on the same WiFi as my dev machine, so localhost:4321 was unreachable.

What I actually wanted was for Claude Code to just show me a screenshot.

Proposal

A screenshot tool (or capability within the sandbox) that can:

1. Start a local dev server (npm run dev, vite, etc.)
2. Open a headless browser (Playwright/Puppeteer) to a specified local URL
3. Capture screenshots at configurable viewport widths (e.g., 1280, 640, 420)
4. Return the images inline in the conversation

Why this matters

Visual QA is the one step that still requires physical access to the machine or a tunneling setup. Everything else in the build-test-verify loop works fine over CLI. This closes the gap.

Scope

This is deliberately narrow — not a general web browsing agent. Just: render a local page, screenshot it, show it to the user. The equivalent of "open dev tools, take a screenshot" but available to the agent.