feat: add template preview cards and --template CLI flag

fix: remove background on heading links in both templates

refactor: split Hero into HeroArticle + HeroPaper with shared heroUtils

fix: left-align headings and remove decorative borders in paper template

feat: agent-friendly project structure and paper template redesign

feat: add article template variant, npx CLI, and llms.txt auto-generation

fix: improve mobile banner layout and PDF print styles

feat: improve PDF export with screenshot-based embed rendering and cover page layout

feat: backport dataviz page, embed export, and visual extraction from smol-training-playbook

update

Clean repository - remove missing LFS files