fix(backend): check if user exists on registration to prevent raw database errors (fix #94)

[Pratyush-Panda-2006]

Description

This pull request prevents raw database validation errors and key constraints leakages when registering a duplicate email account. Previously, the endpoint did not check if the email address was already taken, letting Mongoose throw a raw MongoDB duplicate key constraint violation error (11000) that propagated to the client.

Changes

• Updated backend/src/controllers/userAuth.js to execute await User.findOne({ email }) before creation.
• Returns a clean 400 Bad Request status code with a user-friendly error message if a duplicate user is found.

Fixes #94

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📥 Commits

Reviewing files that changed from the base of the PR and between 87148ba and b48b73c.

📒 Files selected for processing (2)

• backend/src/Utils/Validetor.js
• backend/src/controllers/userAuth.js

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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