Add ResourceLoader to the browser crate that integrates the net, encoding, url, and image crates into a unified resource fetching API: - ResourceLoader wraps HttpClient for HTTP/HTTPS fetching - Content-Type parsing determines resource type (HTML, CSS, image, other) - WHATWG encoding sniffing for HTML (BOM > HTTP > meta prescan > default) - BOM/HTTP charset detection for non-HTML text resources (default UTF-8) - Relative URL resolution via base URL support - HTTP error status handling (4xx, 5xx) - Resource enum: Html, Css, Image, Other with appropriate metadata 30 tests covering MIME classification, text decoding (BOM, HTTP charset, meta prescan, Windows-1252 special chars), URL resolution, and error types. Implements issue 3mhkt6hnbhp25 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>