[UI] 🧹 Revert frontend to a simple welcome page

[ahmdkaml]

🧹 Problem

The frontend has evolved into a full application UI during the Angular → React migration.

For the current stage of the project, this is unnecessary complexity. We want the frontend to return to a simple welcome page while keeping the new React + Vite setup intact.

🎯 Goal

Reduce the frontend back to a minimal welcome page.

The React application should remain fully functional, but the additional application pages, components, and UI should no longer be part of the active frontend experience.

✅ Acceptance Criteria

• The frontend uses React + Vite
• The application starts successfully
• The application displays a simple welcome page
• Unnecessary application UI is removed from the active frontend
• The frontend builds successfully with npm run build
• No Angular code or configuration is reintroduced

📌 Scope

This issue is about simplifying the frontend presentation, not reverting the Angular → React migration.