A complete ARIX SEO Tool for Chrome

Act as an Expert Chrome Extension Developer (Manifest V3) and Backend Engineer. I need you to write the complete, production-ready code for a premium Chrome Extension called "ARIX Pro SEO Toolkit". CRITICAL RULES: 1. NO SCRAPING. Use ONLY official, top-tier SEO APIs. 2. Use Manifest V3, Vanilla JavaScript, HTML, and CSS. No React, no build steps. 3. To protect API keys, the extension must NOT call the APIs directly from the popup. It must call a simple, free Vercel Serverless Function (backen...