- Replace vanilla HTML/CSS/JS with Next.js App Router + React components
- Game logic (champion-data, game-engine, classic-mode) moved to lib/
- UI split into modular components (game-board, champion-search, guess-grid, etc.)
- Add Tailwind CSS v4 with CSS variables for theming
- Immutable state updates, fetch deduplication, next/image for CDN images
- champions.json moved from assets/ to public/