Lazy load pages to reduce main bundle size

[quequeo]

Summary

• Replace static imports of page components with React.lazy() + Suspense for code splitting
• Main bundle reduced from 514 kB to 447 kB (below Vite's 500 kB warning threshold)
• Each page loads as a separate chunk on demand, with a spinner fallback during loading
• Updated App.test.jsx to use async findByText for lazy-loaded components

Test plan

• All 209 tests passing
• ESLint + Prettier clean
• Production build succeeds with no chunk size warnings
• Pre-push hook green