Add a PRD and three prototype directions (Gallery, Command Bar, Guided) behind the prototype picker harness for the lesson Slide embed flow. Covers the top 10 embeddable slide platforms with per-platform detection, link/embed-code normalization, live preview, and How-to-embed docs links.
Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>
