Refactor frontend routing from static to dynamic imports for code splitting

[Smartdevs17]

Description

All frontend routes are eagerly loaded, increasing initial bundle size. Refactor to use dynamic imports with route-based code splitting and prefetching strategies.

Acceptance Criteria

• Route-based code splitting with Next.js dynamic imports
• Prefetching for likely-next routes on hover
• Loading skeletons for async chunks
• Bundle size analysis before/after
• Error boundary for failed chunk loads

Technical Scope

• frontend/app/
• frontend/components/layout/Sidebar.tsx
• frontend/next.config.ts
• Edge: chunk loading failures on slow networks, SEO implications of dynamic loading