Fix Infinite Loading of Invalid CAR Files

[george-hub331]

Fixes #365

Problem

When uploading an empty or invalid CAR file, the UI shows an infinite loading animation without proper error feedback. This creates a poor user experience as users have no indication of what went wrong or how to resolve it.

Changes

• Added basic CAR file validation:
  • Check for empty files before attempting import
  • Improved error messaging
  • Clear file input after failed imports
• Enhanced error display in:
  • Shows clear troubleshooting tips for CAR import failures
  • Added "Okay, take me back to start exploring page" button for better UX
  • Maintains consistent error styling with red-muted background
• Updated error translations to be more descriptive and helpful

Testing

• Upload an empty .car file - should show error message instead of infinite loading
• Upload an invalid file with .car extension - should show validation error
• Verify error message includes troubleshooting tips
• Confirm "take me back" button clears error and returns to explore page
• Check that file input is cleared after failed imports