Remove UnoCSS - Migration Complete

UnoCSS was causing OOM in CI. Removed entirely and replaced with @iconify/vue + plain CSS.

Summary

• Removed UnoCSS plugin from vite.config.ts
• Removed uno.css import from theme/index.ts
• Added @iconify/vue for icons
• Converted all UnoCSS utilities to scoped CSS

Completed

• [x] vite.config.ts - removed UnoCSS plugin
• [x] theme/index.ts - removed import 'uno.css'
• [x] CRoot.vue - @iconify/vue + CSS
• [x] ListItem.vue - @iconify/vue + CSS (spinner, checkmark, close icons)
• [x] CourseLink.vue - @iconify/vue + CSS
• [x] FeaturesList.vue - plain CSS
• [x] Advanced.vue - plain CSS
• [x] Experimental.vue - plain CSS

Test pages

• /guide/features - FeaturesList, ListItem, CourseLink
• /config/projects - CRoot
• /api/advanced/vitest - Experimental

Not used (skipped)

• HomePage.vue - not used in new theme