✨ Feature (chat-message.tsx): single message block rendered in markdown with actions

[KemingHe]

• react-markdown based output rendering
• add code syntax-highlighting
• no borders, use the clean look from GitHub Copilot and Perplexity
• (mock) per-message actions:
  • Perplexity-like left:
    • share publicly (per message, not whole conversation)
    • export (also per message) out to diff formats (dropdown)
    • rewrite (prompt engineering)
  • Perplexity-like right:
    • metadata (type of run, token count, summary, etc.)
    • upvote/downvote rating
    • copy raw md
    • view sources
    • delete
    • report

remember: mobile-first design