HTMLRenderer PDF Bookmark Support

We're looking into using htmlrenderer for our solution and so far we love it, but so far we're unsure of how to add support for bookmarks in pdf. I saw that PDFsharp had it, but I wasn't sure if you also supported it or if you knew of a way to access that functionality.

Start by reviewing the HTML-Renderer PDF generation entry points and how PDFsharp is used, since the issue names no files or tests. Determine whether bookmark support already exists and define the required PDF bookmark behavior before identifying an implementation path. Done means bookmark support is specified, implemented, and covered by a reproducible PDF-level check.

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