✨ feat: add KaTeX support and update theme configuration

- Update @astrojs/mdx and astro dependencies
- Enable KaTeX in theme config for mathematical formula rendering
- Update scrollbar component to hide overflow content
- Add KaTeX mathematical demonstration document
- Update multilingual theme guides to include KaTeX configuration

src/layouts/Layout.astro

@@ -11,6 +11,10 @@ import '@/styles/font.css'
 import '@/styles/global.css'
 import '@/styles/heti.css'
 
+if (themeConfig.global.katex) {
+  await import('katex/dist/katex.min.css')
+}
+
 interface Props {
   postTitle?: string
   postDescription?: string