Review the entire Next.js codebase in app/ and src/ to identify components not using Shadcn UI. Update all components to use Shadcn UI (e.g., replace custom <button> with <Button> from src/components/ui/button.tsx, <input> with <Input> from src/components/ui/input.tsx). Ensure the following:

• Use TypeScript for type safety with explicit prop interfaces.
• Maintain responsive design with Tailwind CSS utilities (sm:, md:, lg:) for consistent styling across devices.
• Centralize Shadcn UI components in src/components/ui/ to avoid duplication.
• Remove custom or redundant CSS in favor of Shadcn UI and Tailwind CSS.
• Ensure accessibility with ARIA attributes and keyboard navigation.
• Simplify component logic to avoid complexity (e.g., use simple hooks like useState instead of custom hooks where possible).
• Update related SSR pages in app/ to reflect changes.
• Handle errors gracefully in the UI using Shadcn UI’s <Alert> for error states.
• Log all updated files and removed code for review.
• Trigger npm run build to verify the updated codebase.