feat: add LaTeX rendering utilities and Tex component

frontend/src/components/Tex.tsx

@@ -0,0 +1,14 @@
+import { renderLatex } from '../utils/latex'
+
+interface TexProps {
+  children?: string | null
+  tag?: keyof JSX.IntrinsicElements
+  className?: string
+  style?: React.CSSProperties
+}
+
+// Safe: renderLatex only produces KaTeX-controlled HTML + HTML-escaped plain text.
+export default function Tex({ children, tag: Tag = 'span', className, style }: TexProps) {
+  const html = String(children ?? '').split('\n').map(renderLatex).join('<br/>')
+  return <Tag className={className} style={style} dangerouslySetInnerHTML={{ __html: html }} />
+}