fix: secure authentication — password hashing + email validation improvements

[Sumukhapb]

Improved Authentication Security

This PR enhances the /signup route by introducing proper security and validation measures.

Key Changes:

• Added bcrypt hashing for storing passwords securely
• Added email format validation to prevent invalid signup data
• Removed sensitive console logs for better security and privacy
• Improved readability and error handling response messages

Why These Changes Are Important

• Storing plain text passwords is unsafe and a major security risk
• Backend should validate email format before creating accounts
• Prevents accidental logging of user credentials in server console

Note
If possible, please add hacktoberfest-accepted label ✅
This contribution aims to improve security and backend reliability for the project.

Thank you for maintaining this repo! 🙌