Frontend Upload Improvements

Solution: Updated frontend/src/components/ComprehensiveImportWizard.js:
  - Increased timeout from 30s to 120s for large file uploads + R2 storage
  - Added console error logging for debugging

Login Session Timeout Fix

1. frontend/src/utils/api.js
  - Added BASENAME constant from environment variable
  - Updated the 401 redirect to use ${BASENAME}/login?session=expired instead of just /login?session=expired

  2. frontend/src/pages/Login.js
  - Added basename constant from environment variable
  - Updated URL cleanup to use ${basename}/login instead of just /login

.env.development

@@ -1,3 +1,3 @@
 REACT_APP_BACKEND_URL=http://localhost:8000
-REACT_APP_BASENAME=/membership
-PUBLIC_URL=/membership
+REACT_APP_BASENAME=/
+PUBLIC_URL=/