Switch shiki themes to catppuccin

First of all, the previously used material palenight did not look good
at all in light mode, so we needed specific themes for dark and light.

Secondly, the catppuccin themes have more symmetry across dark and
light and I think they make some better (though subtle) scoping
decisions.

Author: FichteFoll

docs/.vitepress/config.ts

@@ -185,7 +185,10 @@ export default defineConfig({
     },
   },
   markdown: {
-    theme: 'material-theme-palenight',
+    theme: {
+      light: 'catppuccin-latte',
+      dark: 'catppuccin-macchiato',
+    },
     lineNumbers: true,
     config: md => {
       md.use(markdownItDeflist);