Add ability to fetch and inject web page content into chat as context. Includes SSRF protection (blocks private IPs, localhost), content extraction (strips scripts/styles/nav), and a clean popover UI. Reimplements the concept from PR #1703 without the issues (duplicated ChatBox, dual API routes, SSRF vulnerability, window.prompt UX). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>