Replace highlight.js/lib/common (36 languages) with a curated subset of 16 languages relevant for coding-assistant chat UIs. Both ToolCall (direct hljs) and ChatMessage (rehype-highlight) now share the same custom bundle from src/lib/highlight.ts. Languages included: bash, css, diff, dockerfile, go, ini, javascript, json, markdown, python, rust, shell, sql, typescript, xml, yaml. Markdown chunk: 477KB → 336KB (-30%, -45KB gzipped)