Fixed feedback submission API and CORS issues

[sargamjain5]

Bug Fix: Feedback Submission API & CORS Issues

Issue Fixed

Closes #234

Changes Made

• Fixed feedback submission API connectivity
• Added proper CORS configuration in Express backend
• Fixed frontend API URL handling
• Added .env based frontend API configuration support
• Frontend API URL can now be configured using the REACT_APP_API_URL environment variable
• Fixed MongoDB environment variable setup
• Improved feedback route validation and error handling

Testing Done

• Successfully tested feedback submission locally
• Verified MongoDB database storage
• Verified frontend-backend communication
• Checked for console/API errors

Additional Notes

This fix resolves the issue where feedback submission was failing due to backend API and CORS configuration problems.

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