User-created dynamic doc pages live at /docs/custom/:slug, persisted in the new
backend. The editor offers "Beautify with AI", which regenerates the page as
structured HTML with Mermaid diagrams and replaces the raw markdown source (the
beautified version becomes the page's canonical content and survives edits).
Adds a DocHtml renderer that lazily renders Mermaid blocks, a purple design
token, sidebar/topbar entries for custom pages, and routing.
francy51
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