Modernize app and add Tailwind v4 game mode

[LukeberryPi]

Summary

• upgrade the app to Next 16, React 19, Tailwind 4, modern ESLint/Vitest/Playwright tooling, and CI
• refactor the minigame around typed Tailwind v3/v4 game modes with mode-scoped persistence
• keep Tailwind v3 as the default game while adding a compact opt-in v4 selector
• add ADRs documenting the worker model, game registry, Tailwind v4 migration, framework upgrade, and verification baseline

Verification

• npm install
• npm run typecheck
• npm run lint
• npm run test
• npm run test:e2e
• npm run build
• manual browser check on http://localhost:3000 for v3 default, v4 switch, isolated score state, and visible controls

Notes

• /api/v1 remains compatible and returns the v3 dictionary
• the v4 dictionary starts as v3 parity data with no speculative answer changes
• npm audit reports an upstream production advisory through Next 16.2.9's nested PostCSS dependency; npm's suggested fix is an invalid downgrade to Next 9

[vercel]

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Project	Deployment	Actions	Updated (UTC)
css2wind	Ready	Preview, Comment	Jun 17, 2026 2:00pm