docs: redesign table of content (#12647)

* implement toc

* added to projects

* fixes and adapt for references

* added product frontmatter

* remove action menu from 404 pages

www/apps/user-guide/app/not-found.mdx

@@ -1,3 +1,7 @@
+---
+hide_content_menu: true
+---
+
 import { CardList, H1 } from "docs-ui"
 import {
   BookOpen,
@@ -10,7 +14,7 @@ export const metadata = {
   title: `Page Not Found`,
 }
 
-<H1 hideLlmDropdown>{metadata.title}</H1>
+# {metadata.title}
 
 The page you were looking for isn't available.