Enhancement: Fix markdown formatting for lists in ChatMarkdown

Tailwind CSS v4's Preflight reset applies list-style: none to all ul/ol elements. The `.chat-markdown` CSS in `index.css` adds padding for lists but never restores `list-style-type`, so bullet points and numbers are invisible in all `ChatMarkdown` consumers.

<img width="932" height="774" alt="Image" src="https://github.com/user-attachments/assets/13051074-683b-42b2-b6fc-02c0fcfa69ca" />