feat: standardize API response structure across backend and update frontend handling

[A69SHUBHAM]

Summary

This PR introduces a consistent API response structure across all backend endpoints and updates the frontend to handle the new format.

Changes

• Standardized API responses using a unified format
• Introduced helper functions:
  • success_response(message, data)
  • error_response(message, error)
• Refactored all endpoints to use the new structure
• Ensured consistent HTTP status codes for success and error cases
• Updated frontend to correctly parse and display responses

Why this is needed

Previously, API responses were inconsistent across endpoints, making frontend handling complex and error-prone. This change improves predictability and maintainability.

Testing

• Verified all endpoints return consistent response format
• Tested success and error scenarios
• Confirmed frontend correctly handles new structure

Impact

• Improves code consistency and readability
• Simplifies frontend logic
• Enhances maintainability and debugging

Closes #35