Create src/browse_main.zig as the entry point for the interactive terminal browser.

• Add browdie-browse executable to build.zig with QuickJS dependency
• Add browse build step
• Basic main() that accepts a URL argument and fetches+renders it
• Reuse fetchHttp from fetch_main.zig (make it importable or extract to shared module)
• Wire up htmlToMarkdown and extractLinks from crawler modules