Add @streamdown/math plugin to the chat markdown renderer.
Inline ($x^2$) and block ($$...$$) math both supported with
singleDollarTextMath enabled. Plugin is gated to non-streaming state
to match the existing pattern for syntax highlighting — math renders
when the message completes, avoiding KaTeX re-render churn during
streaming. KaTeX CSS is imported in styles.css; ~30KB CSS + ~430KB
JS added to the bundle. Smoothness improvements during streaming
deferred to a follow-up.
emozilla
71e864b600