SPA Performance Test Implementation

I need to complete a performance test for my studies and want a solid, real-world Single Page Application that showcases advanced JavaScript skills. The app must cover:

• Advanced DOM manipulation
• Data persistence with Local Storage
• API consumption via Fetch with proper promise handling
• Dynamic routing within the SPA
• User authentication with role control (admin and visitor)
• A json-server backend to simulate a database
• Robust validations, consistent error handling, and overall code consistency
• Clean, well-structured code that follows accepted best practices

Correct functionality, clean architecture, and graceful error management are all weighted equally in my assessment. I find API work, auth/role logic, and dynamic routing the toughest areas, so a clear, maintainable approach here is critical.

Environment is fixed: Google Chrome or Firefox, VS Code, Node 18+, and json-server. Please deliver fully commented source code plus a concise README with setup instructions and test credentials so I can run everything locally.