Add LaTeX math rendering to messages

[frinfo702]

Summary

Please add LaTeX math rendering to messages and session transcripts. Coding agents often output mathematical notation, but raw LaTeX is difficult to read in the current UI.

Expected behavior

• Render inline math using $...$ and \(...\).
• Render block math using $$...$$ and \[...\].
• Preserve the original LaTeX source when copying text.
• Fall back to plain text when an expression cannot be parsed.

Example

Inline math:

The energy-mass relation is $E = mc^2$.

Block math:

$$
\int_{-\infty}^{\infty} e^{-x^2} \, dx = \sqrt{\pi}
$$