Add a learn article: $ARGUMENTS

1. File: content/learn/<category>/<slug>.md, where category is one of theming, components, tailwind, best-practices (enforced by content.config.ts).
2. Frontmatter (validated by the learn collection schema):

   ---
   title: "…"
   description: "…" # also used for SEO and cards
   category: theming
   format: guide # guide | reference | tip
   date: "YYYY-MM-DD"
   order: 10 # sort order within the category
   tags: [colors, dark-mode]
   featured: false
   ---
   

3. Writing: follow the document-writer skill (active voice, present tense, task-focused headings). Use MDC components the other articles already use. Code samples must match the current Nuxt UI v4 / Tailwind v4 APIs and this app's export format (useThemeExport).
4. Accuracy: derive palette, font, shade, and radius lists from shared/constants/theme.ts rather than memory. Describe editor controls as they exist in app/components/editor/.
5. Register:
   • Add an item to LEARN_CATEGORIES in app/utils/navigation/learn.ts.
   • Add the route to LEARN_ROUTES in shared/constants/routes.ts (sitemap + prerender; tests/unit/shared/routes.test.ts checks nav ↔ routes).
6. Verify: pnpm vitest run tests/unit/shared/routes.test.ts, then /run-app → /learn/<category>/<slug> renders, the TOC works, and links resolve.