CODE QUALITY: Add error handling and loading states

[jt14den]

Goal

Improve UX by adding proper error handling for failed CSV fetches and loading states for async operations.

Tasks

• Add try/catch in getSheetData.js
• Create error boundary component
• Add loading spinner component
• Show loading state while CSV fetches on lessons page
• Add error message if CSV fetch fails
• Add retry button on error state
• Handle empty/malformed CSV data gracefully
• Add timeout handling for slow networks
• Log errors to console for debugging
• Test with network throttling

User Experience

• Loading: Show spinner with Loading lessons... message
• Error: Show friendly message Unable to load lessons. Please try again.
• Empty data: Show No lessons found matching your criteria

Reference

See STUDENT_README.md Code Quality Tasks

[brainstrom286]

@jt14den sir , kindly check the PR and let me know for any changes to be done .