Improve error handling and UI responsiveness

[dsmithnautel]

Summary

Enhance user experience with better error handling, loading states, and responsive feedback.

Tasks

Error Handling - Backend

• Standardize error response format across all endpoints
• Add descriptive error messages for common failures
• Handle Gemini rate limiting gracefully with clear user message
• Handle MongoDB connection errors
• Input validation with helpful error messages

Error Handling - Frontend

• Global error boundary for React
• Toast notifications for errors and success
• Retry buttons for failed operations
• Clear error messages (not technical jargon)

Loading States

• Skeleton loaders for content loading
• Progress indicators for long operations (PDF processing)
• Estimated time remaining for Gemini calls
• Disable buttons during async operations

Responsive Design

• Mobile-friendly layouts
• Touch-friendly interactions
• Responsive typography and spacing
• Test on various screen sizes

User Feedback

• Success confirmations after actions
• Validation feedback on forms (inline errors)
• Empty states with helpful guidance

Priority

High - critical for good demo and user experience