feat: katex math render for markdown.

[sqhyz55]

No description provided.

[yiboyasss]

Nice improvement!

While testing this locally, I noticed a rendering issue with common shell commands such as: `echo $PATH ` / `echo $HOME`

The `$PATH` / `$HOME` parts are currently interpreted as math expressions and rendered by KaTeX, which breaks the expected display. These patterns are quite common in documentation and code examples.

This happens because the current implementation relies on regex replacement for $...$, which can accidentally match non-math usages of $.

It might be worth considering using a markdown AST-based approach instead, for example integrating math support directly via react-markdown with remark-math and rehype-katex:

import ReactMarkdown from "react-markdown"
import remarkMath from "remark-math"
import rehypeKatex from "rehype-katex"

<ReactMarkdown
  remarkPlugins={[remarkMath]}
  rehypePlugins={[rehypeKatex]}
>
  {markdown}
</ReactMarkdown>